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Energy Converter

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

Decimal places4
  • Joules
    J
    1,000
  • Kilojoules
    kJ
    1
  • Calories (small)
    cal
    239.0057
  • Kilocalories (food)
    kcal
    0.239
  • Watt-hours
    Wh
    0.2778
  • Kilowatt-hours
    kWh
    0.0003
  • British thermal units
    BTU
    0.9478
  • Electronvolts
    eV
    6.2415e+21
  • Foot-pounds
    ft·lb
    737.5621

How to convert energy units

  1. Enter a value

    Type the energy amount you want to convert into the value field.

  2. Pick the source unit

    Choose the unit your value is in, such as joules, kilowatt-hours, or BTU.

  3. Read every conversion

    See the equivalent in all other energy units update live as you type.

  4. Copy what you need

    Copy a single row or copy all conversions at once with the button below.

Why use this tool

Every unit at once

One value converts to joules, kilojoules, calories, kcal, watt-hours, kWh, BTU, electronvolts, and foot-pounds simultaneously.

Handles tiny and huge values

Electronvolt-scale and kilowatt-hour-scale results switch to compact scientific notation so nothing overflows.

Adjustable precision

Slide the decimal places from 0 to 8 to match the accuracy your work needs.

Copy one or all

Copy any single conversion or grab the whole list in one tap for pasting into notes or a spreadsheet.

Runs entirely on your device

Values are converted locally as you type. Nothing is uploaded or stored.

About this tool

The energy converter turns any energy amount into every other common unit at the same time. Enter a value, pick its unit, and joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, electronvolts, and foot-pounds all appear together.

Every unit is defined relative to the joule, the base unit of energy in the metric system. Your input is first converted to joules, then divided out into each target unit, so the whole set stays internally consistent no matter which unit you start from. Food calories are kilocalories, which is why a 200 kcal snack equals 200,000 small calories and about 837 kilojoules.

Energy spans an enormous range, from the electronvolts of a single particle to the kilowatt-hours on a power bill. A British thermal unit, common on appliance and heating labels, is about 1,055 joules, while a foot-pound of mechanical work is roughly 1.36 joules. To keep results readable, very small and very large numbers are shown in scientific notation while everyday values use plain digits with grouped thousands. You control how many decimal places appear, from a rounded whole number up to eight places of accuracy.

Negative energy amounts are rejected and non-numeric input shows a short hint instead of a broken result. For related conversions, try the power converter for rate of energy use, the pressure converter, or the everyday unit converter.

Frequently asked questions

How many joules are in a calorie?
One small calorie equals 4.184 joules, and one food Calorie (kilocalorie) equals 4,184 joules. This converter treats "calorie" as the small calorie and "kcal" as the food Calorie.
What is a kilowatt-hour in joules?
One kilowatt-hour equals 3,600,000 joules, because it is one kilowatt of power sustained for one hour. A watt-hour is 3,600 joules.
Why are some results shown in scientific notation?
Electronvolts are extremely small and kilowatt-hours can be very large in joules. When a number is too tiny or too big to read as plain digits, it switches to compact scientific notation.
Can I convert negative energy values?
No. Energy amounts here are treated as magnitudes, so negative inputs are rejected with a short hint. Enter zero or a positive number.
Is my input sent anywhere?
No. Every conversion happens on your device as you type. Nothing you enter is uploaded, logged, or stored.

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