Electricity units (kWh) explained

1 unit of electricity = 1 kWh = 3,600 kJ. Units = watts × hours ÷ 1,000.

How to work out units

An electricity meter counts energy in kilowatt-hours, called units on the bill. A device rated at 1,000 W (1 kW) running for one hour uses 1 unit.

Multiply the wattage on the device label by the hours it runs, then divide by 1,000. For a month, multiply by the number of days. Actual use can be lower, because many devices (fridges, ACs, heaters) switch on and off.

Monthly units by wattage

Units per month (30 days) = watts × hours per day × 30 ÷ 1,000
Rated power	1 hour/day	4 hours/day	8 hours/day
10 W	0.3 units	1.2 units	2.4 units
60 W	1.8 units	7.2 units	14.4 units
100 W	3 units	12 units	24 units
500 W	15 units	60 units	120 units
1,000 W	30 units	120 units	240 units
1,500 W	45 units	180 units	360 units
2,000 W	60 units	240 units	480 units

Frequently asked questions

How many units does a 1,000 W heater use in an hour?

Exactly 1 unit (1 kWh).

What is the difference between kW and kWh?

kW is power (how fast energy is used); kWh is energy (power × time). Bills charge for kWh.

How many joules is one unit?

3,600,000 joules.

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