There are many units of measurement that aren’t included in any coherent system – and often don’t provide a well-known base unit to help users determine an exact quantity. Some of these, like using a prominent skyscraper as a comparison to estimate the size of similar structures, are commonly heard and don’t require specific measurements.
However, there are some lesser-known and more unusual units of measurement – and a surprising number are still used to this day. While these units may not provide accurate measurements, they often offer additional information about the item being measured.
Roughly the size of the cross-sectional area of a uranium nucleus, a barn measures 10-28 square metres. The name likely came from phrases like “big as a barn” or “hit a barn door,” which were used to describe the uranium nucleus during early neutron-deflection experiments. This unit is actually part of a system of measurement, which includes the microbarn (“outhouse”) and yoctobarn (“shed”).
Prior to the 19th century, farmers in Ireland would use this term to describe the size of their fields – a “cow’s grass” indicated the amount of land that could produce a sufficient quantity of grass to support one cow.
In Guernsey, in the British Channel Islands, a similar unit called a “cow field” is still used to refer to the size of a plot of land. Due to the island’s small size, most parcels are not measured in acres – and a small unit of measurement was necessary.
This term is generally used in the context of astrophysics or nuclear engineering to refer to an especially short period of time. One “shake” is officially defined as 10 nanoseconds.
A “jiffy” was first used in the late 18th century as a slang word for lightning, but was soon adopted by chemists and physicists to measure time. In computer science, this unit describes the duration of one tick of a timer interrupt – typically 0.01 seconds.
Other units of measurement
Banana equivalent dose
In order to help people better understand the severity of exposure to radiation from nuclear weapons or medical procedures, the term “banana equivalent dose” describes the additional dose of radiation a person would absorb from eating one banana. Even without contamination, organic materials naturally contain a small amount of radioactive isotopes – and a “banana equivalent dose” is approximately 78 nanosieverts.
Molar mass of cellulose
This term is used by the pulp and paper industry, which measures the intrinsic viscosity of a pulp sample to determine the molar mass. This viscosity is directly related to the pulp’s weight-average molar mass through the Mark-Houwink equation, but values are generally cited as the “viscosity” of the cellulose.
Mother Cow Index
Real estate in the American Southwest was formerly measured according to the “Mother Cow Index,” which would provide potential buyers with additional information about the parcel of land. Instead of simply measuring the size, the “Mother Cow Index” measured how many pregnant cows an acre of land would support – indicating the land’s agricultural quality, arability, and natural resource availability.