🔋 Energy Converter
Food labels show Calories (kilocalories), physics textbooks use joules, electric bills use kilowatt-hours, furnaces use BTU. And a food Calorie is 1,000 physics calories.
Last updated — conversions use exact ISO unit definitions.
How it works
All energy conversions route through the joule (J), the SI unit. One calorie — the small gram-calorie — equals 4.184 J. But food "calories" are actually kilocalories (kcal), or 1,000 small calories, so 1 food Calorie ≈ 4,184 J = 4.184 kJ.
Kilowatt-hours (kWh) are energy units too, even though the name looks like power. 1 kWh = 3,600,000 J = 3.6 MJ. A 100 W light bulb left on for 10 hours uses 1 kWh. Your electricity bill charges you per kWh.
The BTU (British Thermal Unit) is the amount of energy needed to heat one pound of water by one degree Fahrenheit — about 1,055 J. It's still used for natural gas pricing and furnace ratings in the US. 1 kWh ≈ 3,412 BTU, 1 kcal ≈ 3.968 BTU.
The calorie confusion
A food Calorie (capital C) is a kilocalorie = 1,000 small calories = 4,184 joules. The physics calorie heats 1 gram of water by 1°C. This is why fitness apps use kJ and food labels use Calories.
How accurate are these conversions?
All conversions use ISO 80000 standard unit definitions. For example, 1 inch = 2.54 centimeters exactly by international agreement.
Why can't I see all units on mobile?
The result table scrolls horizontally. The headline pair above shows the most commonly requested conversion.
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No. All calculations happen in your browser. We collect zero personal data.
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