How energy converter works
Energy shows up with a different unit in every field: nutrition labels use kilocalories (the famous "Calories"), electricity bills use kilowatt-hours, heating specs use BTU, physics uses joules, and particle physics uses electronvolts. This converter translates any of the twelve common units into any other.
Every conversion is anchored to the joule using exact or internationally-agreed definitions: one calorie is exactly 4.184 J (the thermochemical definition used on nutrition labels), one kilocalorie is 4184 J, one watt-hour is exactly 3600 J, one BTU is 1055.05585262 J (the International Table value) and one electronvolt is 1.602176634 × 10⁻¹⁹ J (exact, by the 2019 SI redefinition). The tool normalizes your value through joules, so both directions of every pair agree.
Results are reported to 12 significant digits, which keeps tiny values like electronvolts meaningful and large values like gigajoules readable. The intermediate value in joules is shown for every conversion so you can check magnitudes at a glance — for example 1 kWh is 3.6 MJ and 2000 kcal is about 2.32 kWh. All math runs in your browser.