Zerdly

Energy Converter

Convert energy between joules, kilowatt-hours, calories and BTU instantly and for free with this easy browser-based energy converter.

100% FreeRuns in your browserBasic
How to use this calculator

Convert energy

Amount to convert
From (the unit you have)
To (the unit you want)

Result

0.001

1 Joules (J) = 0.001 Kilojoules (kJ)

All units

Joules (J)
1
Kilojoules (kJ)
0.001
Calories (cal)
0.239006
Kilocalories (kcal)
0.000239
Watt-hours (Wh)
0.000278
Kilowatt-hours (kWh)
2.7778e-7
British thermal units (BTU)
0.000948

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the amount you want to convert.
  2. Choose the unit you have (From) and the unit you want (To).
  3. Read the result instantly — every other unit is listed too.

How it works

Converts between kilojoules, joules, kilocalories (1 kcal = 4.184 kJ) and watt-hours (1 Wh = 3.6 kJ).

Worked example

4.184 kJ. = 1 kilocalorie.

Common mistakes

  • Confusing calories (cal) with kilocalories (kcal/Cal) used on food labels.
  • Mixing energy (J) with power (W) — power is energy per second.

Frequently asked questions

Calories or kilocalories?

Food 'Calories' are kilocalories — 1 Cal = 1,000 cal = 4.184 kJ.

How many joules in a kWh?

3,600,000 J (3.6 MJ) in one kilowatt-hour.

How many kilojoules are in a kilocalorie?

4.184 kJ. Food 'calories' are really kilocalories, so 100 kcal = 418.4 kJ.

How accurate are the conversions?

They use standard conversion factors at full device precision, so they're reliable for everyday and professional use.

Does it work offline and stay private?

Yes — the conversion runs entirely in your browser, with no sign-up and nothing sent to a server.

Related tools

Explore more in Units, Measurement & Converters.

Cite this tool

Zerdly. (2026). Energy Converter. Retrieved from https://www.zerdly.com/tools/energy-converter/

Tip: Enter any known values to calculate the remaining results.

All calculations run in your browser. Your inputs are never saved or transmitted.