Rules and Conventions for Writing SI Units

Rules and Conventions for Writing SI Units

1. The units named after scientists are not written with a capital initial letter. E.g. newton, henry, ampere and watt.

2. The symbols of the units named after scientists should be written by the initial capital letter. E.g. N for newton, H for henry, A for ampere and W for watt.

3. Small letters are used as symbols for units not derived from a proper noun. E.g. m for metre, kg for kilogram.

4. No full stop or other punctuation marks should be used within or at the end of symbols. E.g. 50 m and not as 50 m.

5. The symbols of the units are not expressed in plural form. E.g. 10 kg not as kgs.

6. When temperature is expressed in kelvin, the degree sign is omitted. E.g. 283 K not as 283° K (If expressed in Celsius scale, degree sign should be included e.g. 100° C not as 100 C, 108° F not as 108 F).

7. Use of solidus is recommended for indicating a division of one unit symbol by another unit symbol. Not more than one solidus is used. E.g. ms^-1 or m/s. J/K/mol should be JK^-1 mol^-1.

8. The number and units should be separated by a space. E.g. 15 kgms^-1 not as 15kgms^-1.

9. Accepted symbols alone should be used. E.g. ampere should not be written as amp and second should not be written as sec.

10.The numerical values of physical quantities should be written in scienti c form. E.g. the density of mercury should be written as 1.36 × 10⁴ kg m^-3 not as 13600 kg m^-3.