Quite a few of us do not write the SI units correctly. If you are a Physics or Chemisty student, and still remember what you studied in school, you’ll know the importance of getting your units and symbols right.

** Important in SI:**

- The short forms for SI units (such as mm for millimeter) are called
**symbols**,*not*abbreviations.

- SI symbols
*never end with a period*unless they are the last word in a sentence.

**RIGHT:**20 mm, 10 kg

**WRONG:**20 mm., 10 kg.

- SI symbols should be preceded by digits and
*a space must separate the digits from the symbol*.

**RIGHT:**It was 300 mm wide. The millimeter width was given.

**WRONG:**It was 300mm wide. The mm width was given.

- Symbols
*always are written in the singular form*(even when more than one is meant).

**RIGHT:**1 mm, 500 mm, 1 kg, 36 kg

**WRONG:**500 mms, 36 kgs

**BUT:**It is correct to pluralize written-out metric unit names: 25 kilograms, 250 milliliters

- The symbol for a compound unit that is
*a quotient of two units is indicated by a solidus*or by a negative exponent.

**RIGHT:**km/h or km·h^{-1}(for kilometers per hour)

**WRONG:**kmph or kph (do*not*use p as a symbol for “per”.)

**BUT:**It is correct to say or write “kilometers per hour”.

- The meaning of an SI symbol can be changed if you substitute a capital letter for a lower case letter.

**RIGHT:**mm (for millimeter, which means 1/1000 of a meter)

**WRONG:**MM or Mm (M is the prefix for mega, which means one million; a megameter is a million meters)

Links:

potsdam.edu

poynton.com

lamar.colostate.edu

Write to me: Suman[at]sumankumar[dot]com