Numbers and Units/Some Basic Rules for Working with Units

Some Basic Practices Related to Writing About Units

It is common in STEM fields to abbreviate units of scientific measurement.  When writing, it is important to use the correct abbreviations. At best, erroneous abbreviations give the impression that you don’t care about your work, but they also have the potential to confuse your readers.

The table below shows the correct symbols for many commonly used scientific measurements, as well as some of the most important guidelines governing their use in STEM writing.

Scientific Measurement	Symbol
Mass (gram, kilogram)	g, kg
Force/pressure (newton, kilonewton, pascal, hectopascal, kilopascal)	N, kN, Pa, hPa, kPa
Volume (millilitre, litre)	ml, l (L)
Temperature (kelvin, degree celsius)	K, ˚C
Time (millisecond, second, minute, hour, hertz)	ms, s, min, h, hz
Length (millimetre, centimetre, metre, kilometre)	mm, cm, m, km
Electricity (ampere, coulomb, volt, ohm, farad, henry, siemens)	A, C, V, Ω, F, H, S
Magnetism (weber, tesla)	Wb, T
Light Intensity (candela, lux, lumen)	cd, lx, lm
Amount of Substance (millimole, mole)	mmol, mol
Energy (joule, watt)	J, W
Angle (degree, arcminute, arcsecond, radian, steradian)	°, ', ", rad, sr
Radioactivity (becquerel, gray, sievert)	Bq, Gy, Sv
Catalytic activity (katal)	kat
Practices for Appropriate Use	Example
Do not pluralize unit abbreviations.	The chemicals only weighed 46 g.
Only use a period after abbreviations if they end a sentence.	The chemicals only weighed 46 g. Compound A was 30 g lighter than Compound B.
Put a space between numerals and unit abbreviations, unless using angular degrees, arcminutes, or arcseconds. The space practice also applies to degrees Celsius and percentages.	The chemicals only weighed 46 g. Compound A was approximately 20 % as heavy as Compound B before burning at 21 ˚C. The coordinates of the UBC Thunderbirds Baseball diamond are 49°15'21"N 123°14'28"W.
Do not capitalize unit symbols unless they are named after people (e.g. kelvin, joule). Litres have been granted an exception to this practice due to 'l' appearing similar to the number '1' and so can be written as either 'l' or 'L.' Millilitres (and other multiples) should still be written as 'ml.'	The chemicals only weigh 46 g. Absolute zero (0 K) is equal to -273.15 ˚C. Grams are abbreviated to ‘g’ in writing.