What is a kWh?
A kilowatt-hour is the energy used by a 1,000-watt device running for one hour. It equals exactly 3,600,000 joules (3.6 MJ), about 860 kilocalories, about 3,412 BTU, and 1,000 watt-hours. Watts measure how fast energy flows; kilowatt-hours measure how much flowed in total.
Conversions
- 1 kWh = 3,600,000 J = 3.6 MJ
- 1 kWh ≈ 860 kcal (1 kcal = 4,184 J)
- 1 kWh ≈ 3,412 BTU; 1 therm = 100,000 BTU ≈ 29.3 kWh
- 1 kWh = 1,000 Wh; 1 MWh = 1,000 kWh
- 1 litre of petrol ≈ 9.7 kWh of chemical energy
kW vs kWh
kW is a speed, kWh is a distance. A 2 kW heater draws energy twice as fast as a 1 kW heater, but run for half the time both used 2 kWh. Bills charge kWh; fuse boxes and inverters are limited in kW. To turn any appliance label into money: watts ÷ 1,000 × hours × price per kWh.
A feel for the scale
- Phone charge — 0.015 kWh
- Big Mac — 0.65 kWh
- A day of human food — 2.3 kWh
- Boiling 10 litres of water — 1 kWh
- 10-minute hot shower — ~4 kWh
- 100 km in an electric car — 15–20 kWh
- A home — 25–33 kWh per day, 8,000–12,000 kWh per year
Convert your own numbers with the energy unit converter.
Common questions
What is a kWh?
A kilowatt-hour is the energy used by a 1,000-watt device running for one hour. It equals 3,600,000 joules (3.6 MJ). It is a quantity of energy, not a speed — watts are the speed, kilowatt-hours are the distance.
What is the difference between kW and kWh?
kW is power — how fast energy flows right now. kWh is energy — how much flowed in total. A 2 kW heater running for 3 hours uses 6 kWh. Your bill charges kWh; your fuse box limits kW.
How many joules are in a kWh?
Exactly 3,600,000 joules, or 3.6 megajoules. One watt is one joule per second, and an hour is 3,600 seconds.
How many kcal are in a kWh?
About 860 kilocalories. One kcal is 4,184 joules, so 3,600,000 ÷ 4,184 ≈ 860. An adult eating 2,000 kcal a day consumes about 2.3 kWh of food energy.
How many BTU are in a kWh?
About 3,412 BTU. Going the other way, 1 BTU ≈ 0.000293 kWh, and 1 therm = 100,000 BTU ≈ 29.3 kWh.
How many watts are in a kilowatt?
1,000 watts. A kilowatt-hour is therefore 1,000 watt-hours, and a 15 Wh phone charge is 0.015 kWh.
How much is 1 kWh in real terms?
One kWh boils about 10 litres of water, runs a modern fridge for a full day, drives an electric car roughly 5–6 km, or carries about the food energy of one and a half Big Macs.
How do I convert kWh to money?
Multiply kWh by your tariff. At €0.28/kWh, 1,000 kWh costs €280. Every appliance rating in watts can be turned into money: watts ÷ 1,000 × hours × price.