Energy Converter
Convert joules, kilowatt-hours, calories, BTU, and more.
- joules
- kwh
- calories
- btu
- energy
About Energy Converter
Energy is measured in different units depending on whether you're talking about electricity bills, food, physics, or heating. Joules are the SI unit. Kilowatt-hours show up on power bills. "Calories" on food labels are actually kilocalories. British Thermal Units (BTU) are still standard for heating and air-conditioning equipment in the US. Each represents the same physical quantity — the ability to do work — but at wildly different scales.
This converter brings them all into one view so you can compare energy in any common unit. A kilowatt-hour, for example, is 3.6 million joules, around 860 kilocalories, or about 3,412 BTU.
How to use
Enter a value into the input and pick the unit from the dropdown — joules, kilojoules, kilowatt-hours, watt-hours, calories, kilocalories, BTU, foot-pounds, electronvolts, and more. The conversions panel lists the equivalent in every other unit.
Tap any row in the list to swap the input to that unit, or use a row's copy button to lift its value. Useful when sizing a heater (BTU/h × hours), checking a food label (kcal vs kJ), or doing back-of-the-envelope physics (joules to electronvolts).
Frequently asked questions
Are food "calories" the same as physics calories?
No — food calories are kilocalories. The "Calorie" on a nutrition label (often capitalised, or written as "kcal") is 1,000 small-c calories. A 2,000-Calorie daily diet is really 2,000,000 calories in physics units. The kilocalorie row in this converter is the food-label one.
How many joules in a kilowatt-hour?
Exactly 3,600,000 joules — because one watt is one joule per second, and one kilowatt-hour is 1,000 watts × 3,600 seconds. So a typical home using 30 kWh of electricity a day is consuming 108 megajoules.
What is a BTU?
A British Thermal Unit is the amount of energy needed to raise one pound of water by one degree Fahrenheit — about 1,055 joules. BTUs are still standard for heating and air-conditioning capacity in the US; a 12,000 BTU/h air conditioner is roughly 3.5 kW.
Why are electronvolts so much smaller than everything else?
Because they describe single-particle interactions, not bulk energy. One electronvolt is the kinetic energy an electron gains crossing a one-volt potential — about 1.602 × 10⁻¹⁹ joules. Useful for atomic physics and chemistry, where individual molecular bond energies sit in the few-eV range.