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Energy Unit Converter
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Quickly and accurately convert between over 10 energy units including joules, calories, and kWh.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This page converts among seven energy units: joules (J), kilojoules (kJ), calories (cal), kilocalories (kcal), watt-hours (Wh), kilowatt-hours (kWh), and British thermal units (BTU). The joule is the SI unit for energy. Celsius and Fahrenheit are temperature units, and watts and kilowatts are power units; they are not interchangeable with energy without additional information.
The conversion uses a fixed joule factor for each listed unit. In general:
Result in target unit = input value × input-unit factor ÷ target-unit factor
| Unit | Joules per unit used here |
|---|---|
| J | 1 |
| kJ | 1,000 |
| cal | 4.184 |
| kcal | 4,184 |
| Wh | 3,600 |
| kWh | 3,600,000 |
| BTU | 1,055.05585 |
For example, 540 kJ × 1,000 J/kJ ÷ 4,184 J/kcal is about 129.0631 kcal. The displayed number can be rounded to the selected decimal precision.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Type the number whose energy you want to convert.
Choose J, kJ, cal, kcal, Wh, kWh, or BTU. Every displayed result depends on this source unit being correct.
Choose a precision option to control how many decimal places are shown. This changes formatting, not the accuracy of the original measurement.
The page lists the equivalent values in the other supported units. You can copy a result or select one to continue from that value.
As a quick magnitude check, 1 kcal is 1,000 cal and 1 kWh is 1,000 Wh. A result off by roughly a factor of 1,000 often means the source was entered as cal instead of kcal, or Wh instead of kWh.
Use cases
See how the tool fits into real work and everyday tasks.
When two product or technical documents use different energy units, convert each value to a common unit before comparing them. Confirm that both specifications mean the same kind of energy quantity.
Convert a joule or kilojoule result into another supported unit to check the arithmetic and order of magnitude in a worked problem.
Use the kWh and Wh outputs to express an energy amount in another unit. If the question is about power, also use the relevant time interval; energy alone does not determine power.
Q&A
Find concise answers to common questions and confusing cases.
Using this converter's factor, 1 kcal equals 4,184 J, while 1 cal equals 4.184 J. The prefix distinction is a factor of 1,000.
BTU has more than one definition. This page uses 1,055.05585 J per BTU. For a technical specification or contract, use the BTU definition stated in that source.
No. A kilowatt-hour measures energy and a kilowatt measures power. To calculate average power, you also need the time over which the energy was used.
Notes
Review scope, result limitations, and important precautions before use.
The calorie and BTU labels can refer to different defined units. This page uses 4.184 J per cal and 1,055.05585 J per BTU. When precision matters for engineering, procurement, or contractual work, check the unit definition specified by the source document rather than assuming every reference uses these same conventions.
The precision selector controls the number formatting only; additional digits do not add accuracy to the input data or remove differences between unit definitions. This converter handles energy-unit arithmetic only. It does not calculate equipment efficiency, heat loss, or power from an energy amount without a time value.
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