E = mc2 —In SI units, the energy E is measured in Joules, the mass m is measured in kilograms, and the speed of light is measured in metres per second. An object moves at different speeds in different frames of reference, depending on the motion of the observer.

To understand E=mc², you have to define each of the variables. E is the energy of an object at rest, m is that object’s mass, and c is the speed of light in a vacuum. Neither the energy nor the mass of an object can change, although the mass can change forms, such as when an ice cube melts.

E=mc2 is the famous formula that shows the equivalence of mass and energy. Learn how Einstein derived it, what it means and how it relates to nuclear reactions and light speed.

Learn what E = mc² means and how to use it with this calculator. Find out the rest energy, mass and energy equivalence of any object and explore the consequences of Einstein's theory of relativity.

Learn what E=mc2 means in simple terms and some of its consequences. The equation relates energy, mass and the speed of light, and is derived from Einstein's Special Theory of Relativity.

Learn what Einstein's famous equation means and how it relates energy and mass. Find out how the speed of light squared is the conversion factor and why it is so huge.

Einstein’s legendary equivalence between mass and energy, given the simple formula E=mc^2, is familiar even to schoolchildren. At times, it simply stands as a placeholder for science — like in cartoons where writing E=mc^2 on a chalkboard signifies there’s some serious physics going on.

Learn how Einstein showed that energy and mass are different forms of the same thing, and what it means for the world. Explore the history, implications, and examples of E=mc2 with the American Museum of Natural History.

Learn how Einstein's famous equation E=mc2 shows that mass and energy are the same thing, and how this affects time and space. Find worked examples, calculators, and background information on special and general relativity.