When you need this conversion
Watts to kWh conversion is the basis of every energy estimate in solar and home-electrical planning: daily consumption, utility bills, battery sizing, and solar array output all boil down to power multiplied by time. Knowing a device's wattage is only half the picture; you need the hours of operation to know how much actual energy it consumes.
The formula explained
Energy in kilowatt-hours equals power in watts multiplied by the hours it runs, divided by 1000 to convert watts into kilowatts:
kWh = Watts × Hours ÷ 1000
A 24-hour period is a common default for estimating daily use of continuously running loads like refrigerators or routers, but you should substitute the actual runtime for devices that cycle on and off, such as lighting or air conditioning.
Common values at a glance
| Watts | kWh over 24 hours | kWh over 8 hours |
|---|---|---|
| 50 W | 1.2 kWh | 0.4 kWh |
| 100 W | 2.4 kWh | 0.8 kWh |
| 500 W | 12.0 kWh | 4.0 kWh |
| 1000 W | 24.0 kWh | 8.0 kWh |
| 3000 W | 72.0 kWh | 24.0 kWh |
Practical tips
- Use actual run hours, not the full 24, for anything that cycles: a refrigerator compressor might only run 8 to 10 hours a day even though it stays plugged in continuously.
- For solar arrays, "hours" usually means peak sun hours, not daylight hours, since panel output drops well below its rated wattage in early morning and late afternoon light.
- Standby or vampire loads (chargers, set-top boxes, modems) often draw single-digit watts around the clock; over a full day and year that adds up and is worth including in whole-home totals.
- If your appliance wattage varies, such as a fridge compressor cycling or a variable-speed pump, use the average running wattage rather than the peak nameplate figure for a realistic kWh estimate.