Energy Converter - Joules, kWh, Calories, BTU Online

Energy Converter - Joules, Kilowatt-Hours, Calories, and More

Energy appears in many units across physics, nutrition labels, and utility bills. This tool converts between common SI units, electrical energy, thermochemical and international-table calories, British thermal units, mechanical work units, and US therms—everything normalizes through joules (J) for consistent math in your browser.

Units you can convert

SI and derived: joules, kilojoules, megajoules, gigajoules, newton-metres, watt-seconds.
Electrical: watt-hours and kilowatt-hours.
Thermal: IT and thermochemical calories and kilocalories, BTU (IT and thermochemical), US therm.
Mechanical and legacy: foot-pound force, kilogram-force metre, metric horsepower-hour, erg, electron volt.

Definitions used

International table (IT) calories use 4.1868 J per calorie; thermochemical calories use 4.184 J. BTU (IT) follows the international table definition tied to those calories. Electron volts use the CODATA exact value for the elementary charge. These choices match typical engineering references; always confirm against your contract or standard if regulatory precision is required.

Frequently Asked Questions

Why does my food label not match kilocalories exactly?

Labels usually mean kilocalories (often written as Calories with a capital C). Pick kilocalorie IT here unless your document specifies thermochemical values.

Is a watt-second the same as a joule?

Yes. One watt applied for one second delivers one joule of energy.

Can I convert power (watts) with this tool?

This page converts amounts of energy, not power over time unless you multiply power by duration yourself. Use energy units like Wh or kWh for electrical energy.

Are conversions exact?

They use standard conversion factors; display rounding may hide trailing digits. For custody transfer or billing disputes, use certified systems and documented factors.