The following are the rules and conventions for writing SI Units and their symbols:
  • The units named after scientists are not written with an initial capital letter.
Example: newton, henry, ampere and watt.
  • The symbols of the units named after scientists should be written by the initial capital letter.
Example: N for newton, H for henry, A for ampere and W for watt.
  • Small letters are used as symbols for units not derived from a proper noun.
Example: m for metre, kg for kilogram.
  • No full stop or other punctuation marks should be used within or at the end of symbols.
Example: 5 m, and not as 5 m. or 5.m
  • The symbols of the units are not expressed in plural form.
Example: 100 kg, not as 100 kgs.
  • When the temperature is expressed in kelvin, the degree sign is omitted.
Example: 383 K, not as 383° K (If expressed in celsius scale, degree sign should be included, e.g. 100 °C, not as 100 C and 108 °F, not as 108 F).
  • Use of solidus (/) is recommended for indicating a division of one unit symbol by another unit symbol. Not more than one solidus is used.
Examplems1 or m/s. J/K/mol should be JK1mol1
  • The number and units should be separated by a space.
Example: 15 kgms1 not as 15kgms1
  • Accepted symbols alone should be used.
Example: Ampere should not be written as amp, and second should not be written as sec
  • The numerical values of physical quantities should be written in scientific form.
Example: The density of mercury should be written as 1.36×104kgm3, not as 13600kgm3