Energy Unit Converter
How it works
Every unit here is turned into joules first — multiplying by the entered unit's own factor — and then divided back out by each of the seven units' factors. One factor per unit rather than one formula per pair, and the seven answers cannot disagree with each other.
Most of those factors are exact: a kilojoule is 1,000 J by definition of the prefix, a calorie is exactly 4.184 J, and a kilocalorie (food Calorie) is exactly 4,184 J. BTU is the exception — it has a few slightly different historical definitions, and 1,055.06 J is the commonly used International Table figure rather than a defining constant.
Frequently asked questions
Is a "Calorie" on a nutrition label the same as a calorie?
No — and this trips up a lot of people. The capital-C "Calorie" printed on food packaging is actually a kilocalorie, equal to 1,000 of the small calories the unit is named after. A "200 Calorie" snack is 200,000 calories in the strict scientific sense. This converter labels the food-label unit "Kilocalorie / food Calorie" for that reason.
Where does kWh commonly show up?
On electricity bills. Utilities bill by the kilowatt-hour — the energy used by a 1,000-watt load running for one hour — because a plain watt is a rate, not an amount, and a household's usage over a month needs a unit for the total energy consumed, not just the momentary draw.
Where does BTU commonly show up?
On the ratings of heating and cooling equipment in the US — air conditioners, furnaces and space heaters are usually sized in BTU (or BTU per hour, a power rating). It stands for British Thermal Unit, and the 1,055.06 J figure used here is the commonly cited International Table value, one of a few slightly different historical definitions of a BTU.