Energy Converter

About this energy converter

This tool converts between 7 common energy units, spanning physics (joules, kilojoules), nutrition (calories, kilocalories), and everyday electricity and heating (watt-hours, kilowatt-hours, BTU). Pick any two units, enter a value, and the result updates instantly — every conversion happens with simple arithmetic directly in your browser, so there's no network request, no waiting, and it keeps working even if you lose your internet connection.

Common real-world uses

Food labels (kilocalories or kilojoules depending on the country), electricity bills and EV battery capacity (kilowatt-hours), air conditioner and furnace ratings (BTU), and physics or engineering calculations (joules) all measure energy in different units by convention — this tool covers translating between all of them.

Units covered

• Joule (J) — the SI unit of energy, defined as the work done by one newton of force over one meter — a single joule is roughly the energy released dropping an apple one meter.
• Kilojoule (kJ) — equal to 1,000 joules, the unit used on nutrition labels in most countries outside the US alongside (or instead of) Calories.
• Calorie (cal) — the small (thermochemical) calorie, defined as the energy needed to raise 1 gram of water by 1°C — not the unit on food labels, which uses the much larger kilocalorie.
• Kilocalorie (kcal) — equal to 1,000 small calories — this is what a food label actually means by "Calories" (capital C), the standard unit for dietary energy in the US.
• Watt-hour (Wh) — the energy delivered by one watt of power sustained for one hour — commonly used to rate small battery capacities like phone power banks.
• Kilowatt-hour (kWh) — equal to 1,000 watt-hours, the standard unit electric utilities bill you in and the unit used for EV battery capacity and home solar production.
• British Thermal Unit (BTU) — the energy needed to raise 1 pound of water by 1°F — still the standard unit for rating air conditioner and furnace capacity in the US.