Rules for writing SI Units

1. Symbols for units are written without capital letters, except when it is derived from name.
Example:
"t" for time
"h" for hour
"m" for meter


2. Symbols for units derived from proper name are written in capital.
Example:
"A" for ampere
"W" for watt


3.Full names of units are written with lower case letters only.
Example:
newton
henry


4. A space is left between symbols of compound units.
Example:
N m


5. A space is left between the number and symbol.
Example:
56 J
5 A


6. Only one SI prefix is permitted.
Example:
kA
MJ


7. A symbol should not be followed by a fullstop except when it is a product.
Example:
kg.m


8. Numerals with more than three digits shall be written without commas and with a narrow spacing at an interval of three digits.
Example:
45 006
72 674


9. A number with four figures is not broken as mentioned above.
Example:
4321


10. A symbol of a unit is placed after the decimal part of the number.
Example:
40.50V