Unit conversions
 

There is not need for conversions if we use SI units without prefixes. A derived SI unit can often be expressed in different way of base and/or derived SI units with special names. The expression of the same quantities with different prefixes and their conversion does not call for an explanation.

Beside the SI usage it may be need unit conversion because the countries can use units outside SI (units accepted because they are widely used, units to be used within specific area, etc.) all over the world. (Sometimes the conversion in case of an old unit, before SI, is not possible with the required accuracy and perhaps it has changed during the years or it was defined not with the best accuracy.)

We have to refer to international standards (ISO 31-0….31-13 and ISO 1000) and literature primarily in this topic. Nowadays increasingly more websites can be found for unit conversions. They are proper or not, it does not belong to MKEH competence therefore everybody uses it for his own responsibility.

http://www.bipm.fr/en/si/conversions.html
http://www.digitaldutch.com/unitconverter
http://www.chemie.fu-berlin.de/chemistry/general/units_en.html
http://www.megaconverter.com/Mega2/index.html