Energy Converter
Enter an energy amount and its unit to see the equivalent in joules, calories, kilocalories, watt-hours, kilowatt-hours, and BTU.
How energy conversion works
The joule (J) is the SI base unit of energy. A calorie (the small, scientific calorie) is defined as exactly 4.184 J; a food "Calorie" (capital C) is actually a kilocalorie, equal to 1,000 small calories.
A kilowatt-hour (kWh), commonly used for electricity billing, is the energy used by a 1,000-watt device running for one hour — equal to 3,600,000 J. The BTU (British thermal unit), common in the US for heating and cooling capacity, equals about 1,055.06 J.
Frequently asked questions
Is a food Calorie the same as a scientific calorie?
No — a food "Calorie" (capital C, often called a kilocalorie) equals 1,000 small calories (lowercase c). This calculator's "kcal" option is the one that matches food labels.
How many joules are in a kilowatt-hour?
1 kWh = 3,600,000 J, since it's the energy of 1,000 watts sustained for 3,600 seconds (one hour).
Why do US appliances list BTU instead of watts?
BTU is the traditional US customary unit for heating and cooling capacity (like air conditioners and furnaces), while watts are the SI unit more common elsewhere — both measure the same underlying quantity, energy.