Reading an electricity bill
Meters count kilowatt-hours. A 2 kW heater run for three hours uses 6 kWh, which is 21.6 MJ. Tariffs are per kWh, so this is the unit that turns physics into money.
Energy
Convert kwh to joules
1 kilowatt-hour equals 3,600,000 joules. Enter a value below to convert instantly.
Kilowatt-hours to joules connects the unit on your electricity bill to the SI unit of energy. A kilowatt-hour is simply a kilowatt sustained for an hour, so the conversion is 1,000 W × 3,600 s = 3,600,000 J — exactly 3.6 megajoules.
1 kWh
3,600,000 J
Multiply the number of kilowatt-hours by 3600000 to get joules. How this is calculated
Need the other direction? Convert joule to kilowatt-hour →
Formula
Multiply the number of kilowatt-hours by 3600000 to get joules.
Step by step
- Start with 1 kWh.
- Multiply by the conversion factor 3600000.
- 1 × 3600000 = 3,600,000 J.
Kilowatt-hours to Joules conversion table
| Kilowatt-hours (kWh) | Joules (J) |
|---|---|
| 1 | 3,600,000 |
| 2 | 7,200,000 |
| 5 | 18,000,000 |
| 10 | 36,000,000 |
| 20 | 72,000,000 |
| 50 | 180,000,000 |
| 100 | 360,000,000 |
| 500 | 1,800,000,000 |
| 1,000 | 3,600,000,000 |
Where kilowatt-hours and joules are used together
Battery and EV capacity
EV batteries are rated in kWh — a 60 kWh pack holds 216 MJ. Consumption is quoted in kWh per 100 km, which makes efficiency comparisons straightforward within the unit and awkward against a fuel figure in litres.
Solar generation
Panel output is a power rating in watts; generation over a day is energy in kilowatt-hours. A 5 kW array producing for the equivalent of four full-sun hours yields about 20 kWh, or 72 MJ.
Comparing energy sources
Gas is billed in kWh or therms, food energy is in kilocalories, and physics works in joules. Converting everything to joules is the only way to compare them on a common basis.
Everyday kilowatt-hours worth knowing
Values people actually look up, with the reason each one comes up. Every figure is calculated with the same engine as the converter above.
| Kilowatt-hour (kWh) | Joule (J) | What it is |
|---|---|---|
| 0.001 | 3,600 | One watt-hour |
| 1 | 3,600,000 | The base conversion |
| 2 | 7,200,000 | A kettle boiling several times |
| 10 | 36,000,000 | A day's use for a small household |
| 30 | 108,000,000 | A day's use for a large household |
| 60 | 216,000,000 | A mid-size EV battery |
| 100 | 360,000,000 | A large EV battery |
| 300 | 1,080,000,000 | A month of modest household use |
How these two units are defined
The joule is the SI unit of energy: one watt for one second, or one newton acting through one metre. The kilowatt-hour is not an SI unit but is a legitimate composite of SI units, defined as exactly 3.6 MJ. Utilities use it because domestic consumption in joules would run to hundreds of millions. Note the difference between power and energy: a kilowatt is a rate, a kilowatt-hour is an amount. Confusing them is the single most common error in energy arithmetic.
Rounding and precision
The 3.6 MJ definition is exact, so no precision is lost. Meter readings are typically resolved to 0.1 kWh, and energy figures on appliance labels are test-standard values with their own tolerance. When converting to joules the number grows by six orders of magnitude, which makes it easy to present far more significant figures than the input justified — round back to the precision of the original reading.
Mistakes people make with this conversion
-
Confusing kW with kWh
A kilowatt is a rate; a kilowatt-hour is an amount of energy. 'A 5 kW battery' is meaningless — batteries store kWh and deliver kW.
-
Multiplying by 3,600 instead of 3,600,000
That converts kilowatt-hours to kilojoules, not joules. The factor from kWh to J is 3.6 million.
-
Mixing up calories and kilocalories
Food 'calories' are kilocalories. One kcal is 4,184 J, so a 2,000 kcal daily intake is about 8.4 MJ, or 2.3 kWh.
Read more about these units
Sources for this page
- SI Brochure — The International System of Units (SI), 9th edition
- Special Publication 811 — Guide for the Use of the International System of Units (SI)
Content on this page last reviewed 12 August 2026. Spotted an error? Report it — see also how these values are calculated.
Convert Kilowatt-hour to other energy units
1 kWh expressed in every other energy unit on this site.
- Joule J 3,600,000
- Kilojoule kJ 3,600
- Megajoule MJ 3.6
- Gigajoule GJ 0.0036
- Millijoule mJ 3,600,000,000
- Microjoule µJ 3,600,000,000,000
- Nanojoule nJ 3.6e+15
- Attojoule aJ 3.6e+24
- Erg erg 36,000,000,000,000
- Calorie (thermochemical) cal 860,420.65
- Kilocalorie kcal 860.42065
- Calorie (IT) cal(IT) 859,845.23
- Kilocalorie (IT) kcal(IT) 859.84523
- Megacalorie Mcal 0.86042065
- Watt-hour Wh 1,000
- Kilowatt-hour kWh 1
- Megawatt-hour MWh 0.001
- Gigawatt-hour GWh 0.000001
- Watt-second W·s 3,600,000
- Kilowatt-second kW·s 3,600
- Horsepower-hour hp·h 1.3410221
- British Thermal Unit BTU 3,412.1416
- BTU (thermochemical) BTU(th) 3,414.4251
- MBTU (thousand BTU) MBTU 3.4121416
- MMBTU (million BTU) MMBTU 0.0034121416
- Therm (US) thm (US) 0.034129563
- Therm (EC) thm (EC) 0.034121282
- Ton-hour (refrigeration) ton·h 0.28434514
- Foot-pound ft·lbf 2,655,223.7
- Inch-pound in·lbf 31,862,685
- Foot-poundal ft·pdl 85,429,297
- Kilogram-force Meter kgf·m 367,097.84
- Gram-force Centimeter gf·cm 36,709,784,000
- Gram-force Meter gf·m 367,097,840
- Kilogram-force Centimeter kgf·cm 36,709,784
- Ounce-force Inch ozf·in 509,802,960
- Horsepower-hour (metric) PS·h 1.3596216
- Electronvolt eV 2.2469433e+25
- Kiloelectronvolt keV 2.2469433e+22
- Megaelectronvolt MeV 2.2469433e+19
- Gigaelectronvolt GeV 2.2469433e+16
- Hartree Eh 8.2573642e+23
- Rydberg Ry 1.6514728e+24
- Ton of TNT tTNT 0.00086042065
- Kiloton of TNT ktTNT 8.6042065e-7
- Megaton of TNT MtTNT 8.6042065e-10
- Tonne of Oil Equivalent toe 0.000085984523
- Barrel of Oil Equivalent bboe 0.00058844075
- Gigaton of TNT GtTNT 8.6042065e-13
- Fuel Oil Equivalent (kiloliter) FOE (kL) 0.000089557523
- Fuel Oil Equivalent (US barrel) FOE (bbl) 0.00056399035
About the kilowatt-hour
The kilowatt-hour (kWh) is a Metric unit of energy. The billing unit on electricity meters — one kilowatt drawn for one hour.
About the joule
The joule (J) is a SI unit of energy.
Related conversions
Frequently asked questions
How many joules are in a kilowatt-hour?
Exactly 3,600,000 J, or 3.6 MJ. A kilowatt-hour is one kilowatt (1,000 J per second) sustained for one hour (3,600 seconds).
Why do utilities bill in kilowatt-hours instead of joules?
Because the joule is far too small for domestic use — a typical household would consume hundreds of millions of them a day. The kilowatt-hour keeps bills in two- and three-digit numbers.
How much energy is in a 60 kWh EV battery?
60 kWh is 216 MJ. For comparison, a litre of petrol contains roughly 32 MJ of chemical energy — though only a fraction of that reaches the wheels in a combustion engine, which is why the two figures cannot be compared directly.
How do you convert kilowatt-hours to joules?
Multiply the number of kilowatt-hours by 3600000 to get joules.
What is 1 joule in kilowatt-hours?
One joule equals 2.7777778e-7 kilowatt-hours.
When would I convert kilowatt-hours to joules?
This conversion is common when nutrition labels, electricity bills, heating, and physics.