Electrical units and conversion

Watts to kWh calculator

Convert watts to kilowatt-hours using the time a device runs, turn kWh back into average watts over a known duration, and switch between Wh and kWh — with the formula shown for every result.

How do you convert watts to kWh?

Multiply watts by hours of use and divide by 1,000: kWh = W × h ÷ 1,000. A 1,000 W heater running for 1 hour uses 1 kWh; a 500 W device for 2 hours also uses 1 kWh. Time is required because watts measure power (a rate) and kWh measure energy (an amount). Going the other way, average watts = kWh × 1,000 ÷ hours, so 2 kWh used over 2 hours is an average of 1,000 W. Without a duration, kWh cannot be turned into watts.

Your inputs

Conversion

Power

Example wattages

Duration

How long the device draws this power. Watts alone are not energy.

Duration unit

kWh

1,000 W for 1 hours = 1,000 Wh

Exact given your inputs

Energy: 1 kWh
Watt-hours: 1,000 Wh
Power: 1,000 W
Hours: 1

Watts are power, kWh are energy

kWh = watts × hours ÷ 1,000. Reversing it gives an average: a device that cycles on and off can peak far above the average watts shown.

Method

kWh = watts × hours ÷ 1,000
average watts = kWh × 1,000 ÷ hours
kWh = Wh ÷ 1,000 · Wh = kWh × 1,000
hours = minutes ÷ 60 · hours = days × 24

Computed by conversionEngine-1.0.0. Negative values and zero-hour averages are rejected.

Assumptions

Power is treated as constant for the whole duration.
A 'day' in the duration field is 24 hours of running, not a calendar average.
Results are exact; display rounds to at most 4 decimals (2 above 100).

What can change the result?

Devices that cycle (fridges, heaters with thermostats) use less than nameplate watts × hours.
Reversed results are averages: peak draw can be much higher.
Standby power adds energy even when a device looks off.

Worked examples

Watts for several hours → kWh: a 1,500 W space heater for 3 hours = 1,500 × 3 ÷ 1,000 = 4.5 kWh.
Minutes → kWh: a 60 W bulb for 45 minutes = 60 × 0.75 ÷ 1,000 = 0.045 kWh.
kWh over a known duration → average watts: 6 kWh used over 8 hours = 6 × 1,000 ÷ 8 = 750 W on average.
Wh → kWh: a 450 Wh portable battery = 450 ÷ 1,000 = 0.45 kWh (and 0.45 kWh × 1,000 = 450 Wh back).

Watts × hours → kWh reference table

kWh = W × h ÷ 1,000, computed by conversionEngine-1.0.0. Constant power assumed.
Power	1 h	5 h	8 h	24 h
10 W	0.01 kWh	0.05 kWh	0.08 kWh	0.24 kWh
60 W	0.06 kWh	0.3 kWh	0.48 kWh	1.44 kWh
100 W	0.1 kWh	0.5 kWh	0.8 kWh	2.4 kWh
500 W	0.5 kWh	2.5 kWh	4 kWh	12 kWh
1,000 W	1 kWh	5 kWh	8 kWh	24 kWh
1,500 W	1.5 kWh	7.5 kWh	12 kWh	36 kWh
3,000 W	3 kWh	15 kWh	24 kWh	72 kWh

From kWh to dollars

This page calculates energy. To turn kWh into a cost per day, month or year at your own rate, continue to the electricity cost calculator. For the concepts behind the units, read watts vs kilowatt-hours explained.