Energy Converter
Turn any energy into a different unit — joule, kilojoule, calorie, kilocalorie, watt-hour, kilowatt-hour, BTU, and more — using exact, published factors.
Joule-based
Every unit is a fixed multiple of the joule, so the converter pivots through joules for one consistent rule.
Display rounding
Results are shown to six decimal places, so very large or very small conversions may round the last digit.
What is an energy converter?
One value, any unit
An energy converter changes a reading from one unit into another — kWh to BTU, BTU to kWh, joule to kilocalorie, calorie to joule, and back. It works by translating every value through a single shared pivot, the joule (J), so any pair of units converts with one consistent rule. This tool covers the nine units used in physics, nutrition, electricity bills, and engineering: joule, kilojoule, megajoule, calorie, kilocalorie, watt-hour, kilowatt-hour, BTU, and foot-pound.
Energy units share a zero point, so converting is purely multiplicative — scale by the factor in, then by the factor out.
result = value × (J per from-unit) ÷ (J per to-unit)Because the joule is the SI base unit, each unit has a fixed number of joules: 1 kWh is exactly 3,600,000 J, 1 kcal is 4184 J, 1 BTU is about 1055.056 J. The converter turns your value into joules first, then into the unit you want — so a single rule handles every direction.
Suppose you want to convert 1 kWh into BTU.
Convert to joules
Multiply by the kWh factor: 1 × 3,600,000 = 3,600,000 J.Convert out to BTU
Divide by the BTU factor: 3,600,000 ÷ 1055.05585262 = 3412.141633.Read the result
1 kWh converts to 3412.141633 BTU — handy for sizing heating or air-conditioning against an electricity bill.
Energy conversion is a simple ratio, so the everyday anchors are easy to remember. The kilowatt-hour is the unit on your electricity bill: 1 kWh equals 3.6 MJ, about 3412 BTU, or roughly 860 kcal, and it runs a 1000-watt heater for one hour. The food Calorie on nutrition labels is a kilocalorie — 1 kcal is 4184 joules, so a 2000-Calorie daily diet is about 8.4 MJ. BTU appears on heating and air-conditioning equipment, where 1 BTU is roughly the energy of a burning kitchen match. If a converted number looks far off by a factor of a thousand, check that the from-unit and to-unit are not swapped — the swap arrow flips them in one click.
The arithmetic is exact; the limits are about precision and unit definitions.
Precision and which calorie or BTU
The calorie and kilocalorie here are the thermochemical values (1 cal = 4.184 J), and the BTU is the IT value (≈ 1055.056 J); other definitions differ by a fraction of a percent, so a published figure may round slightly differently. The SI multiples, watt-hour, and kilowatt-hour are exact by definition. Results are rounded to six decimal places, so conversions with long decimal tails may lose the last digit. Energy is not power — a kilowatt (kW) is a rate, while a kilowatt-hour (kWh) is the energy used at that rate over an hour, so convert energy here and use the power converter for watts.