Energy Converter
How these units are defined
The joule is the SI unit of energy. The calorie used here is the thermochemical calorie, exactly 4.184 J; a kilowatt-hour is exactly 3.6 MJ; the BTU is the International Table BTU (1,055.05585262 J).
| Unit | Equals |
|---|---|
| 1 Kilojoule | 1,000 Joule |
| 1 Calorie | 4.184 Joule |
| 1 Kilocalorie | 4,184 Joule |
| 1 Watt-hour | 3,600 Joule |
| 1 Kilowatt-hour | 3,600,000 Joule |
| 1 BTU | 1,055.055853 Joule |
Worked examples
- 1 Kilocalorie = 4.184 Kilojoule
- 100 Kilocalorie = 418.4 Kilojoule
- 2,000 Kilocalorie = 8,368 Kilojoule
- 2,500 Kilocalorie = 10,460 Kilojoule
Common mistakes
- Food "Calories" (capital C) are kilocalories: a 250 Calorie snack contains 250 kcal, or 1,046 kJ.
- kW is power and kWh is energy: a 2 kW heater running for 3 hours uses 6 kWh.
- The International Table calorie (4.1868 J) is slightly larger than the thermochemical calorie (4.184 J); engineering steam tables use the former.
Energy conversions
Frequently asked questions
How do I convert calories to kilojoules?
To convert kilocalories (food calories) to kilojoules, multiply by 4.184. For example, 100 kcal = 418.4 kJ.
What is a BTU?
A British Thermal Unit (BTU) is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. 1 BTU equals approximately 1,055 joules.
What is a kilowatt-hour?
A kilowatt-hour (kWh) is a unit of energy equal to using 1,000 watts for one hour. It is the standard billing unit for household electricity.
Sources for these factors
- Guide for the Use of the International System of Units (SP 811), Appendix B: conversion factors — NIST
- The International System of Units (SI Brochure), 9th edition — BIPM
Last reviewed against these sources. An automated check recomputes every factor from its definition on each build. How we check accuracy