The m = E/c² calculator compute uses Einsteins Special Relativity formula to compute the mass of an object, given the Energy (E) of an mass at rest and the speed of light (c).
INSTRUCTIONS: Choose units and enter the following:
E - Energy that exists in a mass at rest.
Mass from Energy (m): The calculator returns the mass in kilograms. However, this can be automatically converted to compatible units via the pull-down menu.
A helpful and more detailed explanation can be found at http://www.emc2-explained.info/Emc2/Basics.htm