kWh to Joules Converter
Type kilowatt-hours to get joules. One kWh is exactly 3.6 million joules (3.6 MJ).
1 kWh =
3,600,000J
1 kilowatt-hour is 3,600,000 joules.
- 1 kWh
- 3,600,000 J
- 1 J
- 2.778 × 10⁻⁷ kWh
How to convert kWh to joules
Multiply kilowatt-hours by 3,600,000. A kilowatt-hour is a power of 1,000 watts kept up for one hour, and an hour is 3,600 seconds; a watt is one joule per second, so 1,000 × 3,600 = 3,600,000 joules, exactly.
Megajoules are easier to read: multiply kWh by 3.6. A dishwasher cycle of 2.5 kWh uses 2.5 × 3.6 = 9 MJ, which is 9,000,000 J.
The odd factor comes from the hour. Watts and joules are SI units but the hour is not, so any unit built on it carries the 3,600 seconds inside. Physics formulas expect joules, which is why you convert before using an energy in a calculation.
joules = kilowatt-hours × 3,600,000
- NIST lists the kilowatt-hour as exactly 3.6 × 10⁶ J. Source: NIST SP 811, Appendix B.8: conversion factors by unit.
How to estimate kWh to joules in your head
Think in megajoules and use 3.6 as “a bit more than three and a half”. 4 kWh is 14.4 MJ. Then add six zeros only if someone wants plain joules.
For watt-hours, the same trick gives kilojoules: a 15 Wh phone battery holds 15 × 3.6 = 54 kJ.
Going back, divide megajoules by 3.6, or multiply by 0.28 for a quick figure: 100 MJ is about 28 kWh (exactly 27.78).
kWh to joules and megajoules
From one watt-hour to a megawatt-hour, in joules and the handier megajoules.
| Kilowatt-hours (kWh) | Joules (J) | Megajoules (MJ) | Example |
|---|---|---|---|
| 0.001 | 3,600 | 0.0036 | one watt-hour |
| 0.01 | 36,000 | 0.036 | |
| 0.015 | 54,000 | 0.054 | a phone battery (15 Wh) |
| 0.1 | 360,000 | 0.36 | a 2 kW kettle for 3 minutes |
| 0.25 | 900,000 | 0.9 | |
| 0.5 | 1,800,000 | 1.8 | |
| 1 | 3,600,000 | 3.6 | one unit on an electricity bill |
| 2 | 7,200,000 | 7.2 | |
| 3 | 10,800,000 | 10.8 | |
| 5 | 18,000,000 | 18 |
Show all 14 rowsShow fewer
| 10 | 36,000,000 | 36 | |
| 24 | 86,400,000 | 86.4 | 1 kW running all day |
| 100 | 360,000,000 | 360 | |
| 1,000 | 3,600,000,000 | 3,600 |
Frequently Asked Questions
How many joules are in 1 kWh?
Exactly 3,600,000 joules, or 3.6 megajoules. It follows from 1 kW = 1,000 J per second and one hour = 3,600 seconds.
Why do electricity bills use kWh instead of joules?
Because it matches how we use power: a 1 kW heater running for one hour uses 1 kWh. The same energy in joules is a seven-digit number, which is awkward on a bill.
How many kWh is a megajoule?
One megajoule is 1 ÷ 3.6 = 0.2778 kWh. Gas and fuel energy is often given in MJ, so dividing by 3.6 puts it on the same scale as an electricity bill.
How many joules does a 100 watt bulb use in an hour?
100 W for 3,600 seconds is 360,000 J, which is 0.1 kWh. Ten such hours make one kilowatt-hour.