Benchmark quantities

Benchmark Values for (Nearly) Any Type of Physical Quantity

When encountering the unfamiliar in terms of the very large or the very small, this page is meant to help put the unfamiliar into perspective. For example, people know that a million miles (or kilometers) is a very long distance. But what is it comparable to? You probably 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 to the size of our galaxy ... or 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?

Besides distances, 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 is given in terms of S.I. (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 used for the distances to other objects within the solar system as well. Still larger distances are well represented by using light-years.

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.

Value, in Seconds	Alternative Units	Description
5.39 x 10-44		Planck time
1.1 x 10-10		Period of cesium-133 hyperfine transition used to define the second
1.6 x 10-9		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 satellite at 400 km altitude
8.64 x 104		1 Day
2.4 (2.5) x 106	27.3 (29.5) days	Orbital period of the Moon (Synodic period, or period of the Moon's phases)
3.16 x 107	1 Year	Orbital period of Earth
2.4 x 109	76 years	Human lifetime (typical)
7.8 x 109	248 years	Orbital period of Pluto
1.2 x 1013	380 x 103 years	Age of the universe when neutral hydrogen atoms formed
6.2 x 1015	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