Energy Converter

Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and foot-pounds. Calculates in your browser.

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About energy conversions

Enter a value and choose the units to convert between. Each energy unit is defined against a single base unit, so any pair lines up consistently, the table shows your value in every energy unit at once.

What this does

An energy converter changes an amount of energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and foot-pounds.

How to use it

  1. Enter a value and pick its unit.
  2. Choose the unit to convert to.
  3. Read the converted result instantly.
  4. Swap the units to reverse the conversion.

How it works

Each value is converted to joules first and then to the target unit. The food Calorie on labels is a kilocalorie (1,000 small calories, or 4,184 joules) so the capital C matters.

1 kWh = 3,600,000 J

Example

One kilowatt-hour is 3.6 million joules. A 100-Calorie snack holds about 418,400 joules of energy.

Sources & methodology

Last updated .

Frequently asked questions

What is a food Calorie?

The Calorie on food labels is a kilocalorie, 1,000 small calories, or 4,184 joules.

How many joules are in a kilowatt-hour?

One kWh is 3.6 million joules (3,600,000 J), since a watt is one joule per second.

Is my data stored?

No. Everything is calculated locally in your browser.