Almost every small appliance in your house — phone chargers, lamps, laptops, routers, space heaters — lists its power draw in watts, not kilowatts. Your electricity bill, on the other hand, is priced in kilowatt-hours. This calculator bridges that gap directly: enter a wattage and a run time, and get the kilowatt-hours consumed, without doing the unit conversion in your head first.
Watt to kWh Formula
The division by 1000 converts watts into kilowatts before multiplying by time. A 100-watt bulb running for 10 hours: (100 × 10) ÷ 1000 = 1 kWh.
Common Watt to kWh Conversions
| Watts | Hours | kWh |
|---|---|---|
| 100 W | 10 hrs | 1 kWh |
| 500 W | 4 hrs | 2 kWh |
| 1000 W | 1 hr | 1 kWh |
| 1500 W | 8 hrs | 12 kWh |
Key fact: 1000 watts = 1 kW. Most household appliance labels list wattage directly, so this is often the first conversion you'll need before working out kWh.
Reading Watts Off an Appliance Label
Look for a sticker or plate on the back, bottom, or power cord of the device — it usually lists "W" or "Watts" alongside voltage and amperage. If only amps and volts are given, multiply them together to get watts (Watts = Volts × Amps), then use that in the calculator above.
Frequently Asked Questions
How do I convert watts to kWh?
Multiply watts by hours used, then divide by 1000.
How many kWh is 1000 watts run for 1 hour?
Exactly 1 kWh.
Why do I need to divide by 1000?
Because kWh is based on kilowatts, and there are 1000 watts in a kilowatt.
Where do I find an appliance's wattage?
On the nameplate or label, usually on the back or bottom of the device.
For a broader reference across all power units, see the kW to kWh calculator or the power unit converter.
