Kilowatt-hours and joules
A kilowatt-hour is 1,000 watts for one hour: exactly 3.6 million joules. Electricity bills, EV batteries and appliance energy labels use kWh.
The joule is the SI unit of energy: the work done by a force of one newton over one meter, or one watt for one second. Physics, engineering and EU food labels (as kJ) use joules.
Worked example
Convert 1.5 kWh: 1.5 × 3,600,000 = 5,400,000, so 1.5 kilowatt-hours is 5,400,000 joules. Likewise 2 kWh = 7,200,000 J.
Estimating in your head
The factor is a short exact number, so mental math needs no rounding: multiply by 3,600,000.
Going the other way
To convert joules to kilowatt-hours, divide by 3,600,000 (or multiply by 2.77777777778 × 10^-7).
How this works
J = kWh × 3,600,000
1 kWh = 3,600,000 J and 1 J = 1 J, both by definition, so the factor is their ratio: 3,600,000 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many joules are in a kilowatt-hour?
1 kilowatt-hour = 3,600,000 joules, exactly. The value follows from the unit definitions, so it never changes.
How do I convert kilowatt-hours to joules?
Multiply by 3,600,000. For example, 2 kWh × 3,600,000 = 7,200,000 J.
What is 10 kWh in joules?
10 kWh = 36,000,000 J. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- BIPM — The International System of Units (SI Brochure), 9th edition
- Wikipedia — Calorie
Reviewed Oct 17, 2026 · test vectors fixtures/units/energy/kwh-to-joules/