Energy converter
Convert energy between joules, kilowatt-hours, calories and BTU.
Fill in the fields and the result will appear here automatically.
Converts energy between joules, kilojoules, megajoules, watt-hours, kilowatt-hours, calories, kilocalories, BTU and electronvolts. Kilowatt-hours appear on electricity bills, kilocalories on food labels, BTU on heating and air-conditioning equipment.
How it works
Formula and logic
Every unit converts through the joule using exact defined factors.
Example
One kilowatt-hour is exactly 3,600,000 joules, and one kilocalorie is exactly 4184 joules.
Fields and units
- Energy — in the selected source unit
- From unit — list option
- To unit — list option
How to use
- — Enter the value.
- — Pick the source unit.
- — Pick the target unit.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- BIPM: SI Brochure, version 4.01 (2026) NIST: conversion-factor tables, Appendix B.9
- Limitation
- The result is a rounded unit conversion. Check the entered value and selected units.
FAQ
Why is a kilowatt-hour 3,600,000 joules?
A watt is one joule per second, so a kilowatt for one hour is 1000 × 3600 joules.
Is a food calorie the same as a calorie here?
A food "Calorie" is a kilocalorie. Pick kcal for nutrition labels, cal for the small thermochemical calorie of 4.184 J.
Which BTU is used?
The International Table BTU: 1 BTU = 1055.05585262 J. A thermochemical BTU is a different unit, about 1054.350 J; temperature-specific definitions also differ. Check the definition in your source.
Why is the electronvolt shown in exponential form?
It is about 1.6 × 10⁻¹⁹ joules, so positional notation would need nineteen leading zeros.