Universal Energy Converter

Convert across many related units. Enter your value and which unit it uses.

There are two calorie columns here and they do not carry the same factor. The one labelled cal uses 4.184 joules; the th_cal column uses 4.19002. That 0.14 percent gap is not a bug — the calorie was defined several incompatible ways before SI settled the matter, and older literature rarely says which one it meant. Read whichever matches the definition your source used, and do not treat the columns as interchangeable. The rest of the table anchors on the joule: a kilowatt-hour is exactly 3,600,000 J, an erg is exactly 1e-7 J, and the electronvolt is exactly 1.602176634e-19 J since the 2019 SI redefinition fixed the elementary charge. The BTU is 1055.06 J, itself one of at least three competing definitions that sit within about a tenth of a percent of each other. The trap in everyday use is nutrition labelling: a food Calorie with a capital C is a kilocalorie, so a 250-Calorie snack belongs in the kcal column, not the cal one, a factor-of-1000 mistake. And energy is not power — this page has no time dimension anywhere, so a kilowatt-hour of stored energy tells you nothing about the kilowatts a device draws.