Abbreviations for most units of measurements use small letters and periods. The few exceptions that use capital letters are noted below. Temperature abbreviations use capitals because they come from proper nouns. Measures of mass or weight of types of tons are usually capitalized when abbreviated.
Abbreviations for metric units, including temperatures (Kelvin or Celsius), do not end with periods. Non-metric units with “per” (such as “miles per hour”) usually do not take periods, either.
Temperature abbreviations are used in all types of writing. Other abbreviations of measurements are limited to lists, charts, technical writing, and informal writing. In standard formal English, they are spelled out.
If you spell out the number, spell out the unit of measurement.
There is no need to add an s to an abbreviation to show a plural. This is sometimes done in advertising (“3 lbs. for a dollar”), but it is not necessary.
English Unit Abbreviations
Abbreviation Unit of Measurement
F., F Fahrenheit
fl. oz. fluid ounce
gr., gro. gross
k., kt. karat
k., kt. knot
LT, L.T. long ton
mph miles per hour
n.m. nautical miles
rpm revolutions per minute
T., T ton
T. tablespoon in some cookbooks
t. teaspoon in some cookbooks
The single hatch mark ‘ can stand for foot or a geographical minute (a minute of longitude or latitude). The double hatch mark ” can stand for inch or geographical second (a second of longitude or latitude). So 5’6″ would mean five feet, six inches. 42¡24’54” N. would mean 42 degrees, 24 minutes, 54 seconds north.
Abbreviation Unit of Measurement
C Celsius, Centigrade
cc or cm_ cubic centimeter (cm_ is standard)
G,GB gigabyte (GB is standard)
g, gr gram (g is standard)
K, KB kilobyte (KB is standard)
M, MB megabyte (MB is standard)
mcg or µg microgram ( µg is standard)
MT metric ton
t, T metric ton
w, W watt (W is standard)
kw, kW kilowatt (kW is standard)
kwh, kWh kilowatt-hour (kWh is standard)
Since the metric system uses standard prefixes, you can easily figure out most other metric abbreviations; for example, cl would be centiliter.
The Greek letter µ (mu) is often used to show the prefix micro, especially in scientific publications. For example, µg would be the same as mcg, and µl would be microliter. When by itself, µ stands for micron. This term has recently been superseded by micrometer or µm. Some users still prefer the word micron so it is not confused with the measuring device which is also known as a micrometer, though when pronounced, the accent is on the second syllable. mµ means millimicron, and µµ means micromicron (a millionth of a micron). These terms have largely been superseded by nanometer and picometer, abbreviated nm and pm respectively.
The prefix nano means “billionth,” and is usually represented by the letter n, as in ns for nanosecond.
To abbreviate most square and cubic units in the metric system, add the exponent _ for square and the exponent _ for cubic. For example, m_ means square meter, and mm_ means cubic millimeter. If you use this notation, use it consistently: Use cm_ rather than cc for cubic centimeter.
In standard scientific notation, the word per is represented by a virgule. So km/h is kilometers per hour.
For international standards including abbreviations for very tiny and very large units, see http://physics.nist.gov/cuu/Units/ or http://physics.nist.gov/cuu/Units/checklist.htm.