Benchmark quantities

Benchmark quantities are numbers that can help people gain perspective for any type of measurement. For example, people know that a million miles (or kilometers) is a very long distance. But what familiar thing is it comparable to? A person may know that it's larger than a typical continent, or than Earth itself. But is it comparable to the distance to the Moon, or perhaps to the Sun? Or to the nearest star other than the Sun? Or perhaps to the size of our galaxy, or to the distance to the nearest galaxy? Likewise, one millionth of an inch (or of a centimeter) is certainly small, but is it most comparable to the size of an atomic nucleus, a whole atom, a virus, or perhaps a single-celled organism? Similar questions can be asked about very fast or very slow speeds, very large or small masses, or time spans, or temperatures, ... and many other types of physical quantities.

Every quantity listed in this article is given in terms of the International System of Units (SI), which are metric units. In some cases, alternative units are given if they are in common use. For example, the distance between Earth and the Sun, besides being given in meters, is also one Astronomical Unit (AU) by definition, and the AU is commonly used for distances to other objects within the solar system as well. Still larger distances are better represented by using light-years.

Note: This article uses the U.S. convention for naming the numbers 10⁹ and larger. For example, 1 billion denotes 10⁹ ("1" followed by 9 zeroes), 1 trillion denotes 10¹², and 1 quadrillion denotes 10¹⁵.

Acceleration

Acceleration is the rate at which an object's velocity changes. The SI unit of acceleration is meters per second squared (m/s²), or, equivalently, "meters per second, per second." Alternative units are in terms of the acceleration g of objects falling due to gravity on Earth, where g is 9.8 m/s².

Value, in meters per second squared	Alternative Units	Description
1 x 10-5 10 millionths	1 millionth of 1 g	Variation in gravitational acceleration for 3 m (10 foot) change in elevation near Earth or, variation in g aboard an orbiting space ship/station
0.0027	0.028% of g	Gravitational acceleration of the Moon due to Earth's gravitational field
0.0059	0.060% of g	Gravitational acceleration of Earth or the Moon due to the Sun's gravitational field
0.05	0.5% of g	Variation in gravitational acceleration on Earth (equater vs. poles, at sea level)
1.6	g/6	Gravitational acceleration on the Moon
9.8	1 g	Gravitational acceleration on Earth
50	5 g	Acceleration at which humans typically lose consciousness
450	46 g	Highest acceleration survived by a human Don't try this at home! People have also not survived at lower accelerations than this!
10,000-30,000	1000-3000 g	Typical lab centrifuge

Density

Density is a measure of how compact a material substance is. It is calculated by dividing the total mass of a material sample by the sample's volume. Density can be thought of as a combined effect between how close together the atoms in a material are, as well as how massive the individual atoms are. In solids and liquids, the atoms or molecules are closer together than in a gas, so are considerably denser than gases such as air or helium.

There is a limit to how closely atoms can be packed together under normal conditions, so there is a limit to how high a normal material density can be. Achieving higher densities then requires special conditions, for example, those found in the core of a star, or, going even more extreme, inside an atomic nucleus or neutron star.

The SI unit of density is kilograms per cubic meter (kg/m³). Alternative units are grams per cubic centimeter (g/cm³). Since water has a density of 1 g/cm³, using these units also gives the ratio of a material's density to that of water.

Quick scale: While the Sun is, on average, only 40% denser than water, its core is 160 times denser than water. Common metals such as steel, copper, and lead are around 10 times denser than water, which is 800 times denser than air. Helium is roughly 1/7 the density of air.

Quick scale for exotic matter: Atomic nuclei and neutron stars are about 100 trillion times denser than water, which is about 2 septillion times denser than dark matter in our galaxy. (100 trillion is 1 followed by 14 zeroes. 2 septillion is 2 followed by 24 zeroes.) These differences are considerably greater than the ratio between the densest solids and the lightest gas, which is about 250,000 for osmium vs. hydrogen at atmospheric pressure and room temperature.

Value, in kilograms per cubic meter	Alternative Units	Description
2.2 x 10-27		Dark matter, average for universe
4-5 x 10-22		Dark matter, near solar system
6 x 10-22		Dark matter, in Milky Way halo
1 x 10-12 1 trillionth		Air, ultra-high vacuum conditions (10-9 mbar or 10-12 atm)
0.18		Helium, 20 C and atmospheric pressure
1.2		Air, 20 C and atmospheric pressure
9.0		Compressed air, 20 C, 96 psig (111 psia or 7.5 atm abs.)
250	0.25 g/cc	Balsa wood
534	0.534 g/cc	Lithium, the lowest-density solid element
1000	1 g/cc	Water
1400	1.4 g/cc	Sun (average)
2200-3400	2.2-3.4 g/cc	Typical rocks
2700	2.7 g/cc	Aluminium
5500	5.5 g/cc	Earth (average)
8000, 9000, 11,400	8, 9, 11.4 g/cc	Steel, copper, lead, respectively
13,000	13 g/cc	Earth's inner core
22,600	22.6 g/cc	Osmium, the densest element
160,000	160 g/cc	The sun's core (est.)
~1 x 109		White dwarf star
~1 x 1017		Neutron star or atomic nucleus

Dimensionless values

A dimensionless value is simply a pure number. Examples include the fraction of air molecules that are oxygen (0.21 or 21%), the number pi (3.14159...), and Avogadro's number (6.02 x 10²³. A dimensionless value might represent a fraction or percentage of some total, a ratio between two quantities such as the masses of the proton and the electron, or a total count (e.g., the population of a country, or the number of molecules in a glass of water).

Being a pure number, a dimensionless value or quantity has no associated units such as meters or kilograms. For large numbers that represent a total count, the number can alternatively be represented as a multiple of another number, for example two dozen (2x12 or 24), four score (4x20 or 80), a gross (144), or a mole (6.02 x 10²³). For small numbers, alternate units can be given in terms of percent (%), parts per million (ppm), parts per billion (ppb), or parts per trillion (ppt).

Quick scale: Loosely speaking, numbers can be classified as either very small compared to the number 1, comparable to 1, or very large compared to 1.

Value	Alternative Units	Description
Composition of air
0.0004	0.04%, 400 ppm	Fraction of air molecules that are carbon dioxide (0% humidity)
0.009	0.9%	Fraction of air molecules that are argon (0% humidity)
0.006, 0.023, 0.073	0.6%, 2.3%, 7.3%	Fraction of air molecules that are water vapor at 100% humidity and temperatures of 0, 20, 40 C (32, 68, 104 F), respectively
0.21	21%	Fraction of air molecules that are oxygen (0% humidity)
0.78	78%	Fraction of air molecules that are nitrogen (0% humidity)
0.25-0.3	25-30%	Efficiency of a typical thermodynamic heat engine
1	100%	One. Unity. The multiplicative identity.
3 (approx.)		The numbers pi (3.14159...) and e (2.71828...)
3		The number of quarks in a proton or neutron
8		The number of planets in the solar system
22-23		The number of revolutions the Sun has made around the galaxy
208		The number of protons and neutrons, combined, in a nucleus of lead-208, the heaviest stable atomic nucleus
4.6 x 106 4.6 million		Median population of a state in the U.S.A. 2023: average of Louisiana and Kentucky, the 25th- and 26th-most populous states, respectively
3.7 x 107 37 million		Population of Tokyo (2018), the most populous city in the world
3.1 x 108 310 million		Population of the USA (2010 census)
7.9 x 109 7.9 billion		Population of the world (2021)
1 to 4 x 1011 100 to 400 billion		Estimated number of stars in the Milky Way galaxy
6 x 1023	1 mole	Avogadro's number The number of hydrogen atoms in 1 gram, or the number of carbon-12 atoms in 12 grams
9.9 x 1024	16 moles	The number of molecules in 10 fluid ounces (300 ml) of water
10100		1 googol: The number 1 followed by 100 zeros.

Distance, length, height

Distance, length, and height are what may typically come to mind upon hearing the phrase "take a measurement".

The SI unit of length is the meter (m). Alternative units include:

Angstroms

Inches

Feet

Miles

Astronomical units (AU)

Light years

Parsecs

Regarding distances that might be described as "far away," we typically use miles or kilometers to describe distances on Earth, astronomical units for distances within the solar system, and either light years or parsecs for distances to objects outside the solar system.

Quick scale: The Sun's diameter is about 100 times that of Earth, which is about 8 million times bigger than the height of a typical person. A person's height is about 250 times the size of a housefly, which in turn is about 60 million times bigger than the diameter of an atom of hydrogen.

Value, in meters	Alternative Units	Description
1.8 x 10-15		Diameter of a proton (hydrogen nucleus)
1-1.2 x 10-14	10-12 fm	Diameter of nucleus for heavy atoms
5.3 x 10-11 53 trillionths	0.53 Angstroms	Radius of hydrogen atom (Bohr model)
3 x 10-8 30 billionths	30 nm	rhinovirus (cold virus) diameter
0.8-1.2 x 10-7 80 to 120 billionths	80-120 nm	Influenza virus diameter
0.2-3 x 10-7 20 to 300 billionths	20-300 nm	Virus diameter (typical range)
4-7 x 10-7 400 to 700 billionths, or around half of one millionth	400-700 nm	Wavelength range of visible light
0.1-600 x 10-6 0.1 to 600 millionths		Bacterium
1-2 x 10-5 10 to 20 millionths	0.01-0.02 mm, 0.0004-0.0008 inches	Amoeba (typical)
1 x 10-4 100 millionths	0.1 mm, 0.004 or 1/250 inch	Human hair thickness (typical)
6-7 x 10-3	6-7 mm, 1/4 inch	Housefly length (typical)
1.5-1.8	5-6 feet	Human height (typical)
25	82 feet	Blue whale length
527	1729 feet	Sears Tower height (to top of antenna)
8800	29,000 feet, 5.5 miles	Mount Everest, height above sea level
9000-13,000	30,000-42,000 feet, 6-8 miles	Cruising altitude for commercial aircraft
4 x 106 4 million	4000 km, 2500 miles	North America, width at approx. 40 degrees North latitude; Los Angeles-to-New York distance
1.3 x 107 13 million	13,000 km, 7900 miles	Earth's diameter
3.0 x 108 300 million	190,000 miles	One light-second, the distance that light travels in one second
3.8 x 108 380 million	240,000 miles	Earth-Moon distance
1.4 x 109 1.4 billion	870,000 miles	The Sun's diameter
1.5 x 1011 150 billion	1 Astronomical Unit (AU) 93 million miles 150 million km	Earth-Sun average distance
4.5 x 1012 4.5 trillion	30 AU	Sun-Neptune distance
9.46 x 1015	1 light-year 63.2 thousand AU	The distance that light travels in one year
3.09 x 1016	3.26 light years	1 parsec
4.0 x 1016	4.2 ly	Sun-Proxima Centauri distance
8.6 x 1017	91 light years	Geometric mean of distances to 20 brightest stars, excluding the Sun (One measure of a "typical" distance to the brighter stars in the sky)
3.2 x 1018	340 light years	Mean of distances to 20 brightest stars, excluding the Sun (Another measure of a "typical" distance to the brighter stars in the sky)
9.5 x 1020	100,000 light years	Diameter of our galaxy, the Milky Way
1.5 x 1021	160,000 light years	Distance to Large Magellanic Cloud
2.4 x 1022	2.5 million light years	Distance to Andromeda galaxy

Electric current

Electric current is a measure of the movement of electric charges in an electronic circuit. It represents the amount of charge, per unit time, that moves past a fixed location in a circuit.

The SI unit of electric current is the ampere (A) or amp, which is equivalent to 1 coulomb per second. I.e., one amp represents one coulomb of charge moving past a fixed location every second. One milliamp (mA) is one one-thousandth of an amp.

Value, in amps	Alternative Units	Description
0.01	10 mA	Current through typical LED indicator light
0.5		Current in 60 W, 120 V light bulb
15		Current limit in typical household circuit breaker (U.S.A)
Several hundred		Current to start an automobile

Electric field

Electric field can be thought of in two ways. Ultimately, it is tied to the force exerted on charged objects by other charged objects.

One way to think of electric field is the amount of force exerted per unit of charge in a region of space. So, if the field is 5 newtons per coulomb in some region of space, then an object with a charge of 1 coulomb would experience a net force of 5 newtons (a little over 1 pound) from other charged objects. An object with a charge of 2 coulombs would experience twice the force of an object with 1 coulomb.

A more common way to express electric fields is in terms of the change in electrostatic potential per unit of distance. As such, the same 5 newtons-per-coulomb field can also be expressed as 5 volts per meter. In other words, the electric potential changes by 5 volts over a distance of 1 meter. However, as fields are rarely uniform over distances as large as a meter, it is more common to use smaller distances to express the field, such as volts per centimeter (V/cm) or, in a rare mix of SI and Imperial units, volts per mil, where 1 mil is 0.001 inches.

The SI unit of electric field can be expressed as either volts per meter (V/m) or newtons per coulomb (N/C), though it is more common to use V/m. Alternative units of V/cm or V/mil are also commonly used.

Quick scale: In the Bohr model of the hydrogen atom, the electric field is nearly 200,000 times higher than the breakdown field in air (field required to cause sparking or arcing). This in turn is 30,000 times higher than the electric field normally found near Earth's surface -- which helps explain why most of the time we are not experiencing a lightning storm.

Value, in volts per meter	Alternative Units	Description
100	1 V/cm	Typical field near Earth's surface
9000		Field (rms) between prongs of 120 V plug
3 x 106 3 million	80 V/mil	Breakdown field for air at 1 atmosphere pressure
1 to 3 x 107 10 to 30 million	300 to 800 V/mil	Typical dielectric strengths of plastics
5 x 1011 500 billion		Field due to the proton on the electron in a hydrogen atom (Bohr model, ground state)

Electric potential difference, a.k.a. voltage

Electric potential difference, or voltage, is the difference in electrical potential between two points, such as the positive and negative poles of a battery or other device that generates a flow of electrons, or between a point in a device and an electrical ground.

The SI unit of electric potential difference is the volt (V). This unit is used almost universally. Another unit, the statvolt, is used in some textbooks on electricity and magnetism.

Quick scale: A typical Van de Graaff generator has a voltage over 1000 times that of a household outlet, which has a voltage of roughly 10 to 100 times that of typical batteries.

Value, in volts	Alternative Units	Description
1.5		Alkaline battery (AAA, AA, C, D cells)
12		Automobile battery (Six 2-volt cells)
120 (AC)		Household wall outlet (U.S.)
Several hundred thousand		Typical Van de Graaff generator

Electrical resistivity

Value, in ohm-meters	Alternative Units	Description
1.7 x 10-8		Copper
109 or greater		Glass

Energy

Energy can have many different forms, for example heat, light, and sound. Kinetic energy is the energy an object has by virtue of its motion; the more massive or faster an object is, the more kinetic energy it has.

The SI unit of energy is the joule (J). Alternative units include:

electron-volts (eV)

megaelectron-volts (MeV)

calories and Calories (with lowercase or uppercase "c")

british thermal units (BTU)

kilowatt-hours (kW-h)

Value, in joules	Alternative Units	Description
9.4 x 10-25	5.9 x 10-6 eV	Hyperfine energy difference in the ground state of a hydrogen atom
6.1 x 10-21	0.038 eV	Energy of cesium-133 hyperfine transition used to define the second
1.60 x 10-19	1 eV	One electronvolt
2.8 x 10-19	1.8 eV	Low energy of visible-light photon (red, 700 nm wavelength)
5.0 x 10-19	3.1 eV	High energy of visible-light photon (violet, 400 nm wavelength)
2.2 x 10-18	13.6 eV	Energy to ionize a hydrogen atom
8.2 x 10-14	0.5110 MeV	Electron rest-mass energy
1.5 x 10-10 150 trillionths	938.3 MeV	Proton rest-mass energy
5 x 10-5 50 millionths		Kinetic energy of housefly flying (12 mg, 3 m/s)
4.2	1 calorie (with lowercase "c")	One calorie, or the energy needed to raise the temperature of 1 gram of water by 1 C.
70		Kinetic energy of human walking (80 kg, 1.3 m/s or 3 mph)
1055	1 BTU	One British thermal unit
2400		Kinetic energy of 0.22 caliber long-rifle bullet (40 g, 346 m/s)
4200	1 Calorie (with uppercase "C") or 1000 calories (with lowercase "c")	One "food Calorie", or the energy needed to raise the temperature of 1 kilogram of water by 1 C.
4300		Kinetic energy of human world-class sprinter (80 kg, 10.4 m/s)
11,000	0.003 kW-h	Electrical energy in a battery: AA cell (1.5 volts, 2000 mA-hours)
0.99 x 104 99,000		Energy to melt "10 fluid ounces" (300 g) of ice Note: 10 fluid ounces of water are produced after melting. This is the same energy needed to raise the temperature of liquid water by 80 C or 143 F.
1.2 x 105 120,000		Energy to heat 10 fluid ounces (300 g) of liquid water from 0 C to 100 C (32 F to 212 F)
6.7 x 105 670,000		Energy to boil 10 fluid ounces (300 g) of water
3.6 x 106 3.6 million	1 kW-h	One kilowatt-hour A good example benchmark to answer the question: How small is one joule of energy? Answer: A kilowatt-hour of electricity typically costs around 10 cents (ballpark value). A joule of electricity then costs less than one-millionth of that. So a joule is a really small amount of energy.
2.2 x 108 220 million		Energy consumed by 60 W filament lightbulb in 1000 hours lifetime.
3.7 x 109 3.7 billion		Potential energy of satellite-Earth system: 1000 kg satellite at 400 km altitude
2.9 x 1010 29 billion		Kinetic energy of 1000 kg satellite in 400 km altitude low-Earth orbit This is roughly eight times the potential energy of raising the satellite to this altitude.
9.0 x 1016		Rest-mass energy of one kilogram of mass
1 x 1019		Annual electrical consumption of USA (1999)
1.8 x 1032		Difference in kinetic energy of Earth at perihelion and aphelion (relative to the Sun) Difference in potential energy of Earth-Sun system at perihelion and aphelion
2.65 x 1033		Kinetic energy of Earth, in the Sun's rest frame
-5.30 x 1033		Gravitational potential energy of the Sun and Earth, relative to infinite separation

Force

Force is an interaction between two objects, and quantifies how strongly two objects either push or pull on each other. Two objects always push (or pull) on each other with the same amount of force -- a fact that can be difficult to fully grasp, but is in fact the third law in Newton's three laws of motion.

The SI unit of force is the newton (N). Alternative units are pounds-force (lbf), not to be confused with pounds, which are a unit of mass.

Quick scale: The force of gravity between the Sun and Earth is about 6 x 10¹⁹ times the weight of a typical person, i.e. the force of gravity between Earth and a person. A typical person's weight is about 8 billion times stronger than the force between an electron and proton in a hydrogen atom.

Value, in newtons	Alternative Units	Description
8.2 x 10-8		Force between an electron and proton in a hydrogen atom (Bohr model)
450-1100	100-240 lb (force)	Typical person's weight
2.0 x 1020		Gravitational force between Earth and the Moon
3.5 x 1022		Gravitational force between Earth and the Sun

Frequency

Frequency is the repetition rate at which cyclical (repetitive) phenomena repeat.

This section is for cyclical or periodic phenomena other than those involving rotations or revolutions, which are covered in the section "speed, angular or rotational"

The SI unit of frequency is the hertz, which is the number of cycles per second of the repeating phenomenon, for example the 50 or 60 cycles per second used for common household electricity. Alternatively, it can be expressed in terms of the repeat-time period, for example "once every 12 hours and 25 minutes" in the case of ocean tides.

Quick scale: The frequency of a visible light wave is about 4 to 7 million times greater than that of a typical FM radio wave, which is about 500 thousand times greater than that of household electricity, which in turn is near the low end of audible sound frequencies.

Value, in hertz	Alternative Units	Description
2.2 x 10-5 22 millionths	Once every 12 hours and 25 minutes	Ocean tides
50 or 60		Household electrical outlet
20 - 20,000		Audible sound
1 x 106 1 million		1000 kHz AM radio frequency
1 x 108 100 million		100 MHz FM radio frequency
2.45 x 109 2.45 billion		Microwave oven frequency
9.19 x 109 9.19 billion		Frequency of cesium-133 hyperfine transition used to define the second
4.3-7.5 x 1014 430 to 750 trillion		Frequency of visible light (700-400 nm wavelength)

Magnetic field (a.k.a. magnetic flux density)

Most of us are familiar with magnets in our everyday lives. This section lists the strengths of various magnetic phenomena.

The SI unit of magnetic field strength is the tesla (T). Alternative units are in gauss (G).

Quick scale: The magnetic field strength used for an MRI is between 50 to 300 times stronger than a common household refrigerator magnet, which in turn is 300 times stronger than Earth's magnetic field.

Value, in tesla	Alternative Units	Description
2.5 to 6.5 x 10-5 25 to 65 millionths	0.25 to 0.65 G	Earth's magnetic field at Earth's surface (0.25 G near the equator, 0.65 G near the poles)
0.01	100 G	Common household refrigerator magnet
0.5 to 3		Field used for MRI
45		Highest human-made magnetic field, continuous use
100		Highest human-made magnetic field, repeatable pulses (0.015 second pulse duration)

Mass

Mass is the quantity of matter that comprises an object. Strictly speaking, mass is different than weight, which is the strength of the force (or "pull") of gravity on an object. A person standing on the Moon has the same mass, but less weight, than they do when standing on Earth. This is because a person has the same amount of matter wherever they are, but the Moon pulls on them with less gravitational force than Earth does.

The SI unit of mass is the kilogram (kg). Alternate units include:

milligrams (mg)

grams (g)

avoirdupois ounces (oz), not to be confused with fluid ounces

pounds (lbs)

solar masses

Quick scale: The Sun's mass is about 300,000 times that of Earth, which is of order 10²³ -- i.e., 1 followed by twenty-three 0s -- times that of a typical person. A typical person is about 6 million times more massive than a housefly, which in turn is of order 10²² times more massive than an atom of hydrogen.

Value, in kilograms	Alternative Units	Description
9.1 x 10-31		Electron
1.7 x 10-27	1836 times the mass of the electron	Proton, or hydrogen atom
3.5 x 10-25		Lead-208, the heaviest stable atomic isotope
1.2 x 10-5 12 millionths	12 mg	Housefly
0.040	40 g	Standard-velocity 0.22 caliber bullet
0.30	300 grams, 10.4 ounces	10 fluid ounces of water
4-8	10-20 lbs	House cat
75	165 lbs	Human (typical)
1-2 x 105 100,000 to 200,000	200,000-400,000 lbs, 100-200 tons	Blue whale
6 x 109 6 billion	13 billion lbs	Great Pyramid at Giza, Egypt
6 x 1010 60 billion	130 billion lbs	Three Gorges Dam, Hubei province, China
5 x 1018	1 x 1019 lbs	Earth's atmosphere
1.4 x 1021	3 x 1021 lbs	Earth's oceans
7.3 x 1022		The Moon
6.0 x 1024		Earth
1.9 x 1027		Jupiter
2.0 x 1030	1 solar mass	The Sun
1.5 x 1031	7.5 solar masses	Betelgeuse, a supergiant star
1.3 x 1032	65 solar masses	Total mass of binary black hole system in first-ever detection of gravitational waves (2015)
8.2 x 1036	4.1 x 106 solar masses	Black hole at center of Milky Way galaxy
1 x 1040	6-7 x 109 solar masses	Black hole in M87, the first black hole ever imaged (2019)
1 x 1042	5 x 1011 solar masses	Milky Way galaxy (our galaxy)
2-3 x 1042		Local group of galaxies
2-3 x 1045		Local (Virgo) supercluster of galaxies

pH

The pH of an aqueous (water) solution is a measure of the degree of acidity of the solution. It is generally assumed that the solution is near room temperature, or more specifically at 25 degrees Celsius (77 degrees Fahrenheit).

pH is indicated by a numerical scale, with "7" indicating a neutral solution. Acidic solutions have a pH less than 7, while basic solutions have a pH greater than 7.

pH is a measure of the concentration of hydrogen ions. This concentration, in moles per liter of solution, can be found by raising 10 to the power of the negative of the pH value. For example, a pH of 2 indicates a hydrogen ion concentration of 10^-2, or 0.01, moles per liter. A pH of 6 indicates a hydrogen ion concentration of 10^-6, or one millionth, moles per liter.

A more extensive version of the following table appears in the main pH article.

pH value	Alternative Units moles/liter	Description
2	0.01 1 hundredth	Lemon juice, vinegar
3	0.001 1 thousandth	Orange juice
5	0.00001 10 millionths	Black coffee
7	0.0000001 1 tenth of 1 millionth	Distilled water, neutral solutions
11		Household ammonia
14		Drain cleaner

Power

Power can be thought of as the rate at which energy is either produced or consumed. Strictly speaking, energy can be neither created nor destroyed, so in reality power is the rate at which energy is converted from one form into another.

The SI unit of power is the watt (W), equivalent to the production or consumption of one joule of energy every second. Alternate units include the horsepower (1 hp = 746 W) and the british thermal unit per hour (1 BTU/hr = 0.293 W).

Quick scale: The total power radiated by the Sun, if converted to electricity with 100% efficiency, would be enough to power several quadrillion (10¹⁵) large cities of 1 million people each. A city that size consumes the equivalent of 20-30 million traditional lightbulbs in electricity, or 20-30 bulbs per person.

Value, in watts	Alternative Units	Description
0.001	1 mW	Power in beam of a typical laser pointer
0.5 - 1.0		Power output of a small DC electric motor (12 V, 0.1 - 0.2 A)
60		Traditional incandescent lightbulb power
250	0.33 hp	Power output of a moderate-sized (1/3 horsepower) electric motor
1000-1500		Typical power consumption of a microwave oven, toaster oven, or electric heater
90,000	120 hp	Power output of a small (120 horsepower) car engine
1-2 x 109 1-2 billion		Typical electrical power consumption for a large U.S. city (pop. 1 million)
2 x 1017 200 quadrillion		Power radiated by the Sun that reaches Earth (About 1/2 of 1 billionth of the total power radiated by the Sun)
4 x 1026		Total power radiated by the Sun

Pressure

Pressure can loosely be thought of as a measure of the force exerted by a gas or liquid on objects in contact with the gas or liquid. It is actually the force per area that is exerted.

The SI unit of pressure is the pascal (Pa), equivalent to one newton of force distributed over an area of one square meter. Other common units are the standard atmosphere (atm), pounds per square inch (psi), millimeters of mercury (mm Hg) or equivalently Torr, and millibar (mbar).

Pressure values can be expressed as either absolute pressure or gauge pressure. Absolute pressure is the actual force-per-area exerted by the gas or liquid. Gauge pressure is the difference of the absolute pressure minus the surrounding atmospheric pressure. Gauge pressure is useful in that it gives the next force (per area) exerted on a container wall with the gas or liquid of interest on one side and the ambient atmosphere on the other, or can also be used to express deviations of air pressure from standard atmospheric pressure. The units for a gauge-pressure measurement in psi are written as "psig," to distinguish it from an absolute pressure measurement.

Quick scale: The pressure used to make synthetic diamond is several hundred million times that of the atmosphere. The pressure in a good laboratory vacuum system is around one trillionth of that of the atmosphere.

Value, in pascals	Alternative Units	Description
1 x 10-7	1 x 10-12 atm 1 x 10-9 mbar	Laboratory ultra-high vacuum conditions
600	0.006 atm	Atmospheric pressure on Mars
34,000	1/3 atm	Air pressure at summit of Mt. Everest (8849 m or 29,032 ft above sea level)
91,000	0.90 atm (-0.10 atm gauge pressure) 910 mbar	Typical category-5 hurricane
98,000	0.97 atm (-0.03 atm gauge pressure) 980 mbar	Typical category-1 hurricane
100,000	1.0 atm 15 psi, 760 mm Hg, 1013 mbar	Atmospheric pressure
700,000 to 800,000	7-8 atm 100-120 psi	Typical workshop air compressor
21 million	200 atm 3000 psi	Standard scuba tank pressure
5 to 6 billion	50 to 60 thousand atm	Pressure used to make synthetic diamond

Speed

In addition to representing the rate at which something moves, speed can also represent the rate at which two objects either approach each other or separate, as in the case of Africa and South America.

The SI unit of speed is meters per second (m/s), and alternative units can be based on any alternative units for time and/or distance. Extremely fast speeds can be given in comparison to the speed of light c, e.g. (2/3)c for two-thirds as fast as the speed of light.

Quick scale: The speed of light is 30 million times faster than a fast human sprinter, and a fast sprinter is 5 billion times faster than the speed at which Africa and South America are moving apart from one another.

Value, in meters per second	Alternative Units	Description
2 x 10-9 2 billionths	6 cm or 2 inches per year	Rate of separation of Africa and South America
1 x 10-7 100 billionths	3 inches per week	Rate at which grass grows (est.)
7 x 10-6 7 millionths		Tip of hour hand on a wall clock (2" length)
2 x 10-4 or 0.0002 200 millionths		Tip of minute hand on a wall clock (4" length)
0.01	1 cm or 0.4 inches per second	Tip of second hand on a wall clock (4" length)
0.03	1 inch per second	Insect walking
1.3	3 miles per hour (mph)	Human walking
6.7	"4-minute mile" 15 mph	Fast human distance runner
10	100 meters in 10 seconds 22 mph	Fast human sprinter
27	60 mph	Automobile highway speed
107	240 mph	Approx. top speed of Indy race car
343	767 mph	Speed of sound (dry air, atmospheric pressure, 20 C temperature) Standard muzzle velocity of 0.22 caliber long rifle
460	1000 mph	Speed of Earth's surface at equator
510	1100 mph	Speed (rms) of air molecule at around room temperature (27 C, 300 K)
1020	2280 mph	The Moon (relative to Earth)
2700	6000 mph	Speed (rms) of a hydrogen atom at around room temperature (27 C, 300 K)
3100	6900 mph	Satellite in geosynchronous orbit (rela. to Earth)
4700	10,500 mph	Pluto (rela. to the Sun)
7670	17,200 mph	Satellite in low-Earth orbit (400 km altitude)
30,000	67,000 mph	Earth (rela. to the Sun)
48,000	110,000 mph	Mercury (rela. to the Sun)
200,000	c/1500 450,000 mph	The Sun (rela. to the center of our galaxy
2.2 x 106 2.2 million	c/137, or roughly 1% of the speed of light	Speed of electron in hydrogen ground state (Bohr model)
2 x 108 200 million	(2/3)c	Speed of light in glass Speed of electronic signal in typical coaxial cable
2.6 x 108 260 million	0.87c	Speed of an object when its kinetic energy is equal to its rest mass energy mc2
3 x 108 300 million	186,000 miles per second	The speed of light, c

Speed, angular or rotational

This section is for rotational (spinning) motion or the revolution (orbiting) of an object about another object. For periodic phenomena that do not involve rotation or revolution, see the frequency section.

Values are given in terms of cycles (rotations or revolutions) per second. Revolutions per minute (rpm) are used as well.

Quick scale: Air molecules at room temperature spin roughly 100 billion times faster than a car engine, which in turn spins one to ten million times faster than Earth about its axis.

Value, in cycles per second (hertz)	Alternative Units	Description
3.17 x 10-8 317 billionths	Once per year	Revolution of Earth about the Sun
1.16 x 10-5 11.6 millionths	Once every 23 hours, 56 minutes, and 4 seconds, or roughly once per day	Rotation of Earth about its axis
0.0167 or 1/60	1 rpm	One revolution per minute
0.556, 0.75, 1.3	33-1/3, 45, 78 rpm	Phonograph records The progression from 78 to 33-1/3 rpm records is a mid-20th-century, analog example of increasing data storage density.
12.5	750 rpm	Car engine, idling
83-100	5000-6000 rpm	Car engine, typical maximum speed
~1012 to 1013 1 to 10 trillion		Typical rotation speed of an air molecule at room temperature

Temperature

While Celsius and Fahrenheit are two commonly used temperature scales, for comparison purposes it is best to use an absolute temperature scale, so Kelvins (K) are the main units in the listings below.

Value, in Kelvins	Alternative Units	Description
0	-273 C, -460 F	Absolute zero
2.7		Cosmic microwave background
4.2 and less		Liquid helium
20 and less		Liquid hydrogen
77 and less		Liquid nitrogen
90 and less		Liquid oxygen
184	-89 C, -128 F	Coldest recorded (natural) temperature on Earth (Vostok Station, Antarctica, on July 21, 1983)
195 and less	-78 C, -109 F	"Dry ice", frozen carbon dioxide
273	0 C, 32 F	Water freezes, or cold weather
293-296	20-23 C, 68-73 F	Room temperature, or mild weather
310	37.0 C, 98.6 F	Human body temperature, or very hot weather
373	100 C, 212 F	Water boils
450	177 C, 350 F	Moderately hot household oven
530	260 C, 500 F	Very hot household oven
770	500 C, 930 F	Faintly red-hot object
970	700 C, 1300 F	Moderately red-hot object
2800	2500 C, 4600 F	Tungsten lightbulb filament (typical), a white-hot object
5800	5500 C, 9900 F	The Sun's surface
10,000	9700 C, 17,500 F	Surface of a blue-hot star. Examples: Sirius is 9940 K. Rigel is 11,000 K.
1.5 x 107 15 million	1.5 x 107 C, 2.7 x 107 F	The Sun's center

Thermal conductivity

Thermal conductivity is a measure of the ability of a material to conduct heat.

The SI unit of thermal conductivity is watts per meter-kelvin, or W/(m•K). This is equivalent to W/(m•°C) since it is differences in temperature that are relevant in calculations that involve thermal conductivity, so kelvins are then interchangeable with degrees Celsius. Alternative units are W/(cm•K) and BTU/(hr•ft•°F).

Quick scale: The thermal conductivity of copper is about 20 times that of a poor metal conductor like stainless steel, which is about 20 times that of glass. Glass is about 40 times more conductive than air.

Values given are for near-room-temperature conditions.

Value, in watts per meter-kelvin	Alternative Units	Description
0.025		Air (1 atm pressure)
0.12-0.33		Common plastics
0.6		Water
1		Glass
16-20		Stainless steel
166-237		Aluminium: 237 is for pure aluminium. 166-200 is for alloys typically used in aluminium heat sinks. Other alloys can be outside the stated range.
400		Copper
2000		Diamond

Time

Note, the repeat periods of cyclical phenomena, like the cycle time of a typical sound frequency, are not generally included here. Doing so would simply repeat information that can be found in the frequency section of this article. An exception is made for the period of rotation or revolution of astronomical bodies such as Earth or the Moon, since these have historically served as standard definitions of time intervals like the day or the year.

The SI unit of time is the second. Alternative units are minutes, hours, days, weeks, months, and years.

Quick scales: The age of the solar system, and by extension Earth, is roughly 60 million human lifetimes. A typical human lifetime is 25 to 30 thousand days or 2 to 2-1/2 billion seconds. One year is roughly π x 10⁷ seconds, or, more precisely, 31.56 million seconds.

Value, in seconds	Alternative Units	Description
1.1 x 10-10 110 trillionths		Period of cesium-133 hyperfine transition used to define the second
1.6 x 10-9 1.6 billionths		Lifetime of the first excited state of a hydrogen atom
0.2		Human reaction time (typical)
1.3		Light travel time, Earth to the Moon (one-way)
500	8.3 minutes	Light travel time, Earth to the Sun (one-way)
5500	92 minutes	Orbital period of satellites at 400 km altitude, a typical low-Earth orbit.
86,400	1 Day	One day
2.36 x 106 2.36 million	27.3 days	Orbital period of the Moon
2.55 x 106 2.55 million	29.5 days	Synodic period of the Moon, or period of the Moon's phases
3.16 x 107 31.6 million	1 Year	Orbital period of Earth
2.4 x 109 2.4 billion	76 years	Human lifetime (typical)
7.8 x 109 7.8 billion	248 years	Orbital period of Pluto
1.2 x 1013 12 trillion	380,000 years	Age of the universe when neutral hydrogen atoms formed
6.2 x 1015	200 million or 0.20 billion years	Orbital period of the Sun around the galaxy
1.4 x 1017	4.5 billion years	Age of the solar system
4.3 x 1017	13.7 billion years	Age of the universe