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What Is a Beard-Second?

G. Wiesen
G. Wiesen

A beard-second is a measurement of length based on the distance that a beard hair grows in one second of time. This is similar, in structure though not in quantitative value, to a light-year, which is a measurement of length equal to the distance that light travels in one year. While a light-year is a very long distance, due to the tremendous speed of light, the beard-second is quite small since hair grows at a very slow rate. The exact length that this equals is the basis for some debate, and some sources cite it at about 10 nanometers (nm) while other sources use only 5 nm.

There are a number of ridiculous or unnecessarily complicated measurements used, often unofficially, in physics and engineering. In quantum physics, and other disciplines that use extremely small measurements of distance and space, one such measurement is the beard-second. There are two different values that can be used for the beard-second, based on the fact that beard follicles can grow at different rates on different people. The larger of the two measurements is 10 nm, while the smaller measurement is 5 nm in length; a nanometer is one-billionth of a meter (m), or about three-billionths of a foot, in length.

Woman holding a book
Woman holding a book

Due to both the silly nature of a beard-second and the fact that it is not perfectly quantifiable as a standard measurement, it is not officially used in science. It can be used, jokingly, in certain scientific and engineering settings, in which it is typically used simply to indicate an extremely small distance. Using the beard-second measurement of 5 nm, then 1 meter would be about 200 million beard-seconds, while a foot would be just under 61 million beard-seconds. Since one year consists of about 31.5 million seconds, using a 5 nm measurement of a beard-second, then a beard grows at about 0.5 feet (about 15 cm) per year.

This is just one of a number of rather silly or unusual measurements that can be used when documenting distances or amounts, including the rather unusual distance known as a “smoot.” One smoot is about 5 feet and 7 inches (170 cm) in length and is based on the height of Oliver R. Smoot, a student at Massachusetts Institute of Technology in 1958. Oliver Smoot was used by his fellow students to measure the length of the Harvard Bridge, which was about 364.4 smoots (just over 2,034 feet or 620 m) in length. Both the beard-second and the smoot can be used as units for conversion in the Google® calculator through the search engine input, which uses the 5 nm value.

Discussion Comments


@pleonasm - These actually sound like really great examples to show high school students, both to put a human face on scientists, and also to deconstruct the idea of measurement.

I really like making my students think about what they are doing and not take anything for granted. Making them measure with different kinds of units is a really good way to make them question the use of ordinary units, so that they always try to use the best one, rather than just using the one that's familiar to them.


This really made me smile, particularly the part at the end about the smoot. It always delights me when scientists are shown to have a sense of humor, since I feel like, all too often, we only see them as very serious and dignified with no capacity to laugh at themselves.

Being able to make fun of their own pedantry with this kind of joke makes them better people.

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