Watts to kWh Calculator
Watts to kilowatt-hours turns a power in watts and a running time in hours into energy: kWh equals watts times hours divided by 1000. Enter the watts, the hours and a price per kWh to see the energy, formula and cost, with a daily and monthly table.
Watts to kilowatt-hours
2.4 kWh
E = P × t ÷ 1000 → 100 W × 24 h ÷ 1000 = 2.4 kWh; at 0.15 per kWh the cost is 0.36.
How to convert watts to kWh
Energy is power multiplied by time. A kilowatt-hour is one kilowatt used for one hour, exactly 3.6 million joules (BIPM, The International System of Units, 9th edition, 2019). So E(kWh) = P(W) × t(h) ÷ 1000.
Worked example: a 100 W device for 24 hours
100 × 24 = 2400 Wh. 2400 ÷ 1000 = 2.4 kWh. At a price of 0.15 per kWh that is 0.36 for the day.
Daily and monthly use for common loads
The wattages are illustrative; use the number on your own device label. The monthly column assumes the device runs for 24 hours a day for 30 days, which overstates devices that cycle or are used part of the day.
| Load | Watts | kWh in 1 hour | kWh in 24 hours | kWh in 30 days (24 h/day) |
|---|---|---|---|---|
| LED bulb | 10 | 0.01 | 0.24 | 7.2 |
| Phone charger | 5 | 0.005 | 0.12 | 3.6 |
| Laptop | 60 | 0.06 | 1.44 | 43.2 |
| Television | 100 | 0.1 | 2.4 | 72 |
| Desktop computer | 200 | 0.2 | 4.8 | 144 |
| Refrigerator (average) | 150 | 0.15 | 3.6 | 108 |
| Microwave oven | 1100 | 1.1 | 26.4 | 792 |
| Space heater | 1500 | 1.5 | 36 | 1080 |
| Hair dryer | 1800 | 1.8 | 43.2 | 1296 |
| Window air conditioner | 1000 | 1 | 24 | 720 |
| Electric kettle | 1500 | 1.5 | 36 | 1080 |
| Router | 10 | 0.01 | 0.24 | 7.2 |
| Ceiling fan | 60 | 0.06 | 1.44 | 43.2 |
| Washing machine | 500 | 0.5 | 12 | 360 |
| Dishwasher | 1200 | 1.2 | 28.8 | 864 |
Watts, kilowatts and kilowatt-hours
Watts measure how fast energy is used; kilowatt-hours measure how much was used. A 1500 W heater running for 2 hours uses 3 kWh. To go the other way and find average watts from a bill, use the kWh to watts calculator, and to find the current a load draws, use watts to amps.
See every converter on the MicroCoulomb home page.
Frequently asked questions
How do you convert watts to kWh?
Multiply the watts by the hours and divide by 1000: kWh = W × h ÷ 1000.
How many kWh is a 100 W bulb for 10 hours?
100 × 10 ÷ 1000 = 1 kWh.
How do I find the cost?
Multiply the kWh by your price per kWh. 2.4 kWh at 0.15 per kWh costs 0.36.
Is a kilowatt-hour a unit of power?
No. A kilowatt-hour is energy. Power is measured in watts or kilowatts.
Updated