Speed of light squared (mass-energy conversion factor)
| Value | 8.987551787368176 × 10¹⁶ J/kg |
| Status | Exact by definition: no uncertainty |
| Source | Derived from the exact SI value of c (SI Brochure, 9th edition, 2019) |
| Categories | Universal & Atomic |
| Unit | Value |
|---|---|
| joule per kilogram | 8.9875518e+16 J/kg |
| kilojoule per kilogram | 89,875,518,000,000 kJ/kg |
| BTU per pound | 38,639,518,000,000 BTU/lb |
| foot pound-force per pound | 3.0068085e+16 ft·lbf/lb |
| joule per gram | 89,875,518,000,000 J/g |
| watt-hour per kilogram | 24,965,422,000,000 W·h/kg |
| calorie per gram | 21,480,764,000,000 cal/g |
| kilocalorie per kilogram | 21,480,764,000,000 kcal/kg |
| megajoule per kilogram | 89,875,518,000 MJ/kg |
| kilowatt-hour per kilogram | 24,965,422,000 kW·h/kg |
Learning zone
Squaring an exact constant leaves it exact: c² = 89 875 517 873 681 764 J/kg, with no uncertainty whatsoever. It is the slope of the mass-energy line, and its size is the whole reason nuclear processes dwarf chemical ones: burning a kilogram of coal releases about 3 × 10⁷ J, while annihilating a kilogram of anything releases 9 × 10¹⁶ J, three billion times more.
Nothing engineered converts mass completely. Uranium fission liberates roughly 0.09 % of the fuel's rest mass, hydrogen fusion in the Sun about 0.7 %: enough for the Sun to shed 4.3 × 10⁹ kg of mass every second as light. The same factor works in reverse and in miniature: the mass defect of a helium nucleus, a mere 0.5 % of its constituents, is what a binding-energy calculation is really weighing.
Mass-Energy Equivalence (E = mc²)
Cite this page
formula.expert. (2026, October 16). Speed of light squared (mass-energy conversion factor). https://formula.expert/constants/speed-of-light-squared