Energy Converter
Convert joules, calories, kWh, BTU, and therms.
This energy converter switches between common energy units - joules, calories, kilowatt-hours, BTU, and therms - each used in different contexts from nutrition labels to electricity bills to heating system ratings.
Enter an energy value in any supported unit, and the calculator returns the equivalent in your chosen target unit.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 3 kWh to BTU | ≈10,236 BTU | 3 × 3,412 ≈ 10,236 BTU. |
| 500 kilocalories to kWh | ≈0.58 kWh | 500,000 calories ÷ 860,421 ≈ 0.581 kWh. |
Key Energy Conversion Factors
1 kilowatt-hour = 3,600,000 joules = 3,412 BTU = 860,421 calories (approximately). These conversions all connect back to the joule, the SI base unit of energy, though everyday contexts often use whichever unit is conventional for that field - calories for food, kWh for electricity, BTU for heating and cooling.
Why Different Fields Use Different Energy Units
Nutrition uses calories (technically kilocalories on food labels), electricity bills use kilowatt-hours, and heating/cooling systems use BTU, each having become the historical convention in that specific industry - since they all measure the same underlying physical quantity (energy), conversion between them is always possible using fixed factors.
How to Use the Energy Converter
- Open the Energy Converter and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the energy converter works.
Frequently Asked Questions
How do you convert kilowatt-hours to joules?
Multiply the kWh value by 3,600,000, since 1 kilowatt-hour equals exactly 3,600,000 joules.
How many calories are in a kilowatt-hour?
1 kilowatt-hour equals approximately 860,421 calories, or about 860.4 kilocalories (the 'Calories' commonly listed on nutrition labels).
Why does a food label say "Calories" with a capital C?
Nutrition labels use 'Calories' (capital C) to mean kilocalories (1,000 small calories), a convention that can cause confusion since it's 1,000 times larger than the scientific 'calorie' unit used in physics and chemistry.
How do I use this energy converter?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Energy Converter calculate?
Convert joules, calories, kWh, BTU, and therms. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this energy use?
The formula is: target = source * conversion factor. The joule is named for James Prescott Joule, whose meticulous 1840s experiments measuring the heat generated by mechanical work established the mechanical equivalent of heat - a foundational result for the law of conservation of energy - while the calorie, still used on nutrition labels today, was defined earlier and independently within thermal science before the joule became the standard scientific energy unit.
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Last updated: September 27, 2026.