Energy Converter

Convert energy between joules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, electronvolts and foot-pounds — free, instant and private. All conversions run in your browser.

How to use the energy converter

  1. Enter a value. Type the amount of energy you want to convert into the Value box — for example, 500 to convert 500 kilocalories.
  2. Choose your units. Pick the unit to convert from and the unit to convert to, then press ⇄ to swap them whenever you like.
  3. Read the result. The converted energy appears instantly, along with a table showing the same amount in every other energy unit.

About this tool

This free energy converter connects the units used across nutrition, electricity, heating and physics. Food labels use kilocalories (the "Calorie" with a capital C), electricity bills are measured in kilowatt-hours, heating and cooling capacity is rated in BTU, and physics uses joules and electronvolts. The joule is the SI base unit, and each other unit is defined against it: 1 calorie is exactly 4.184 J, 1 kWh is 3,600,000 J, and 1 BTU is about 1,055.06 J.

Whether you are comparing the energy in a snack to the electricity used by an appliance, or converting a physics answer from electronvolts to joules, the tool does it in one step and displays the full table for reference. Every calculation happens locally in your browser with JavaScript, so nothing you type is uploaded, and the converter still works if you go offline after loading the page.

Frequently asked questions

Is a food Calorie a calorie or a kilocalorie?

The "Calorie" printed on food labels is actually a kilocalorie (kcal) — 1,000 small calories. So a 250-Calorie snack contains 250 kcal, or about 1,046 kilojoules.

How many joules are in a kilowatt-hour?

One kilowatt-hour equals 3,600,000 joules (3.6 megajoules), because it is one kilowatt of power sustained for one hour (1,000 W × 3,600 s).

What is a BTU?

A British Thermal Unit is the energy needed to raise one pound of water by one degree Fahrenheit — about 1,055 joules. It is widely used to rate furnaces, air conditioners and gas appliances.

How do I convert kilocalories to kilojoules?

Multiply kilocalories by 4.184 to get kilojoules. For example, 500 kcal equals 2,092 kJ. To convert back, divide kilojoules by 4.184.