The following conventions (rules) should be strictly followed while writing SI units.

i) While writing a unit, only its singular form is used. For example, the mass of any substance should be written as kg not kgs. Distances should be expressed in km not in kms, e.g., ten kilogram is written as

10 kg (correct) 10kgs (wrong)

ii) The abbreviations of any unit does not have full stop (.) at the end, unless it appears at the end of a sentence. Therefore, no full stop is placed either in between or at the end of the symbol of the unit. For example,

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Kg kg. cm cm.

(correct) (wrong) (correct) (wrong)

iii) One space is left between the last digit of a numeral and the symbol of the unit. For example,

10 m 10m and 5 g 5g

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(Correct) (wrong) (correct) (wrong)

iv) Words and symbols should not be mixed. For example,

Kilogram per cubic metre kg/m3 kilogram/m3 kg per cubic metre

(correct) (correct) (wrong) (wrong)

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v) With numerals, the symbols of the units should be written. For example,

100 cm one hundred cm 100 centimeters

(correct) (wrong) (wrong)

vi) The names of the units derived from people’s name are written in small letters. For example, the units named after Joule is written as joule (symbol: J). the unit of force named after Newton is written as Newton, (Symbol: N).

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vii) The sign of degree (°) is not written when the Kelvin scale is employed. For example, temperature of 273 Kelvin is written as,

273 K  273°K

(correct) (wrong)