Rules for writing units

1) The symbol of a unit, which is not named after a person, is written in lower letter (small letter). 

Eg: metre (m) kilogram (kg) 

2) The symbol of a unit, which is named after a person, is written with a capital initial letter. 

Eg: newton (N), kelvin (K) 

3) Full name of a unit, even if it is named after a person is written with a lower initial letter. 

Eg: newton, kelvin. 

4) A compound unit formed by multiplication of two or more units is written after putting a dot or leaving a space between the two symbols.

Eg: newton metre — N.m or N m. 

5) A unit in its short form is never written in plural.