How the electricity cost calculator works
Your meter does not count watts; it counts kilowatt-hours, the energy of 1,000 watts flowing for one hour. So the calculator turns the appliance's power into kW, multiplies it by the hours it runs, and multiplies the resulting kWh by the price on your bill. The result is shown in whatever currency your price is in.
Cost = watts ÷ 1,000 × hours per day × days × duty % × price per kWhThe duty percentage handles appliances whose thermostat switches them on and off. A fridge plugged in all day is not drawing its rated power for 24 hours; its compressor typically runs a third of the time. Leave the value at 100% for anything that draws steady power while it is on, such as lighting, a television or a computer.
Worked examples
A 150 W television and games console used 5 hours a day for 30 days consumes 0.15 × 5 × 30 = 22.5 kWh. At 0.30 per kWh that costs 6.75 for the month, 0.225 a day, or about 82 over a year. A fridge-freezer rated at 120 W that runs 35% of the time uses 0.12 × 24 × 0.35 = 1.01 kWh a day and about 368 kWh a year: roughly 110 at a European price of 0.30, or 63 dollars at 0.17 per kWh. A 1,500 W portable heater used 6 hours a day for a 90-day winter uses 810 kWh, which is 138 dollars at 0.17, more than the fridge costs in two years.
Typical power of household appliances
| Appliance | Power while running | Notes |
|---|---|---|
| LED bulb | 5–10 W | Replaces a 40–75 W incandescent |
| Wi-Fi router | 6–12 W | On 24 hours: about 50–100 kWh a year |
| Laptop | 30–65 W | Less when idle |
| Desktop PC with monitor | 150–400 W | Gaming PCs peak much higher |
| 55 in LED television | 70–120 W | Brightness setting changes it a lot |
| Fridge-freezer | 100–200 W | Runs 30–40% of the time |
| Dehumidifier | 200–500 W | Compressor types cycle with humidity |
| Microwave oven | 800–1,200 W | Short use, small cost |
| Kettle | 1,500 W (US) – 3,000 W (Europe) | Boils quickly, so energy per use is similar |
| Portable electric heater | 1,500–2,000 W | Thermostat models cycle once the room is warm |
| Tumble dryer | 2,000–5,000 W | About 2–5 kWh per load |
Getting a realistic number
- The label shows the maximum. Rating plates give peak or input power. A laptop charger marked 90 W may average 30 W, so a plug-in energy meter over a few days gives the truest figure.
- Use the variable price, not the average bill. Divide the energy part of your bill by the kWh used, and leave out the fixed daily standing charge, which you pay whatever you switch off.
- Check time-of-use tariffs. On night or off-peak rates, running a dishwasher or charging at night can cost half the daytime price.
- Do not forget standby. Ten devices idling at 3 W each add up to 30 W around the clock, about 263 kWh a year.
- Heat is the expensive part. Anything that heats water, air or clothes dominates the bill; small electronics rarely do.
Frequently asked questions
How do I calculate the cost of running an appliance?
Multiply the watts by the hours used and divide by 1,000 to get kWh, then multiply by your price per kWh. A 2,000 W heater for 3 hours uses 6 kWh, which costs 1.80 at 0.30 per kWh.
How much does it cost to run a fridge per year?
A modern fridge-freezer uses about 250–400 kWh a year. At 0.17 dollars per kWh that is roughly 40–70 dollars; at 0.30 per kWh it is 75–120.
How many kWh does a 1,500 watt heater use per hour?
1.5 kWh per hour while the element is on. With a thermostat cycling it half the time, average use falls to about 0.75 kWh per hour.
How much electricity does a TV use?
A 55 inch LED TV draws about 70–120 W. Watched 5 hours a day, that is 130–220 kWh a year.
Does standby power really cost much?
Each watt left on all year uses 8.76 kWh. At 0.30 per kWh a device idling at 5 W costs about 13 a year.
Last reviewed: 2026-09-27 · How we calculate