A standard measure of any physical quantity is called as a unit. For example,Volume is a physical quantity and unit to measure it is liters or milliliters. Similarly , weight is measured using kilograms or pounds.Some units has origined naturally and some have been Standardized. Here is a list of large number of unit converters that are being used in many fields like Engineering, chemistry and many more.
International System of units is a global standard for the units. The national and international units of Measures are developed with the metrology science.