Energy Conversion Calculator

Convert energy between joules, calories, watt-hours, kilowatt-hours, and BTU.

Energy value

From unit

To unit

How energy conversion works

This calculator converts an energy value between the units used across physics, nutrition, and household electricity billing. It converts your input to joules (the SI base unit of energy) first, then converts that value into your chosen output unit.

Standard scientific constants are used: 1 calorie (thermochemical) = 4.184 J, 1 kilocalorie (food Calorie) = 4,184 J, 1 watt-hour = 3,600 J, 1 kilowatt-hour = 3,600,000 J, and 1 BTU = 1,055.05585262 J.

This tool is provided for general educational and planning purposes, such as comparing electricity usage, food energy, or fuel energy content. It is not a substitute for a calibrated meter or laboratory instrument.

Last reviewed August 2026