Every appliance has a power rating in watts on its label. Three steps turn that into money:
1. kWh = watts × hours ÷ 1,000 2. cost = kWh × price per kWh 3. monthly cost = daily cost × days used
Or plug the numbers into the Electricity Cost Calculator.
A kWh (kilowatt-hour) is the "unit" on your electricity bill. A 1,000 W appliance running for one hour uses 1 kWh.
Worked examples
The price per kWh varies a lot between countries and tariff slabs, so these examples use a round 15 per kWh. Swap in the rate from your own bill.
| Appliance | Watts | Hours / day | kWh / month (30 days) | Cost at 15 / kWh |
|---|---|---|---|---|
| Oil or fan heater | 2,000 | 4 | 240 | 3,600 |
| Split AC (1.5 ton, at full power) | 1,500 | 8 | 360 | 5,400 |
| Ceiling fan | 75 | 10 | 22.5 | 338 |
| LED bulb | 9 | 6 | 1.6 | 24 |
| Fridge (averaged) | 100 | 24 | 72 | 1,080 |
| Electric kettle | 1,800 | 0.25 | 13.5 | 203 |
The heater, step by step
2,000 W × 4 h ÷ 1,000 = 8 kWha day8 kWh × 15 = 120a day120 × 30 = 3,600a month
Why your real cost is usually lower
The label shows maximum power. Many appliances don't run at maximum all the time.
- Heaters with thermostats switch off once the room is warm. In a small, insulated room, the element may run half the time or less.
- Inverter ACs ramp down once the room is cool and may use well under their rated power for most of the day.
- Fridges cycle on and off. The label's annual kWh figure, if it has one, is more realistic than watts × 24.
The most accurate way to find out: a cheap plug-in energy meter. Run the appliance for a day and read the kWh.
Why it might be higher
- Slab tariffs. Many utilities, including Nepal's NEA, charge more per kWh as your monthly use goes up. Extra use from a heater may land in a higher slab. See how slabs work on your bill before assuming a flat rate.
- Old or undersized ACs run at full power for hours and never reach the set temperature.
- Standby and fixed charges aren't included in the per-kWh maths.
Heater types compared
All resistive electric heaters (oil-filled, fan, ceramic, infrared) turn electricity into heat at essentially 100% efficiency. A 2 kW oil heater and a 2 kW fan heater produce the same heat per kWh. They differ in how they heat:
- Fan heaters warm the air fast. Good for short bursts.
- Oil-filled radiators heat slowly and stay warm. Good for a room you'll sit in for hours.
- Infrared heats you, not the air. Good in draughty spaces.
A heat pump (including a reverse-cycle AC) can deliver 2–4 kWh of heat for every kWh of electricity, which is why it's far cheaper to run in winter. See Heat Pump Running Cost.
Cheapest ways to cut the cost
- Heat or cool the room you're in, with the door closed.
- Each degree matters. Set the AC a degree or two warmer, and the heater a degree or two cooler.
- Use a timer to warm the room before you get up, rather than running the heater all night.
- Seal draughts around windows and doors. That's the cheapest insulation there is.
- Clean AC filters every few weeks during heavy use.
- Use a fan with the AC so you can set a higher temperature and feel just as cool.