Energy Unit Converter
Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kWh and BTU with exact factors.
How it works
joules = value × factor(from) · result = joules ÷ factor(to) (1 kWh = 3,600,000 J, 1 kcal = 4184 J)
Energy in every form — mechanical, electrical, thermal, dietary — converts through the joule. A watt-hour is one watt sustained for 3600 seconds (3600 J), so a kilowatt-hour is 3.6 million joules. The "calorie" on food labels is actually a kilocalorie (4184 J), a thousand times the small thermochemical calorie used in chemistry.
Worked example
Convert 1 kWh to BTU: 1 × 3,600,000 = 3,600,000 J, then 3,600,000 ÷ 1055.056 ≈ 3412.14 BTU. That is the familiar "one kWh ≈ 3412 BTU" figure from heating and cooling specs.
Sources: Joule — Wikipedia
Frequently asked questions
Is a food Calorie the same as a calorie?
A food Calorie (capital C) is a kilocalorie — 1000 small calories, or 4184 joules. So a 2000-Calorie diet is 2000 kcal, roughly 8.4 million joules or about 2.3 kWh of energy.
How many joules are in a kWh?
Exactly 3,600,000 joules (3.6 megajoules), because a kilowatt is 1000 watts and an hour is 3600 seconds. Electricity bills are measured in kWh for this reason.
What is a BTU?
A British thermal unit is the energy to raise one pound of water by one degree Fahrenheit, about 1055 joules. It is widely used to rate heating, air conditioning and gas appliances.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.