Estimate how much electricity an appliance uses and what it costs, from its wattage, daily runtime and your price per kWh.
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A 1,000 W heater used 2 hours a day for 30 days uses 60 kWh, which costs 12 at 0.20 per kWh. A 2,000 W load run for half an hour on 20 days uses 20 kWh, or 6 at 0.30 per kWh.
Watts are divided by 1,000 to get kilowatts, then multiplied by the hours per day and the number of days to give kilowatt-hours. Multiplying those kilowatt-hours by your price per kWh gives the cost, and both figures are shown.
Real consumption varies with duty cycles, standby draw, efficiency and temperature: fridges, air conditioners and heaters switch on and off rather than running flat out. Tariffs, taxes, fixed monthly fees and demand charges are not included, and tiered or time-of-use prices need a separate calculation per band.
Enter the appliance power in watts, how many hours a day it runs, the number of days and your price per kWh. The tool divides watts by 1,000, multiplies by hours and days and then by the price. A 1,000 W heater used 2 hours a day for 30 days uses 60 kWh; at 0.20 per kWh that costs 12. A 2,000 W kettle-style load used for half an hour on 20 days uses 20 kWh, or 6 at 0.30 per kWh.
Low wattage can still add up when a device never switches off. A 5 W standby load running 24 hours a day for a year uses 43.8 kWh, which is 8.76 at 0.20 per kWh. Swapping a 60 W bulb for a 9 W LED used 5 hours a day for 30 days cuts use from 9 kWh to 1.35 kWh, saving about 1.91 at 0.25 per kWh each month. Multiply the saving by the number of bulbs to see the full effect.
The wattage on a label is often the maximum. Fridges, air conditioners and heaters cycle on and off, so a plug-in energy meter gives a more accurate daily kWh figure than rated power. Use the energy charge from your bill rather than the total divided by usage if there is a large fixed monthly fee. Tiered, time-of-use and demand tariffs need separate calculations for each price band. In Japan, appliance catalogs often use 31 yen per kWh as a reference price: 1,500 W for 1 hour on 30 days is 45 kWh, or 1,395 yen.
| Input | Result |
|---|---|
1000 W · 2 h · 30 d · 0.2 | 60 kWh · 12 |
1500 W · 1 h · 30 d · 31 | 45 kWh · 1,395 |
2000 W · 0.5 h · 20 d · 0.3 | 20 kWh · 6 |
5 W · 24 h · 365 d · 0.2 | 43.8 kWh · 8.76 |
60 W · 5 h · 30 d · 0.25 | 9 kWh · 2.25 |
9 W · 5 h · 30 d · 0.25 | 1.35 kWh · 0.34 |
On the appliance label, in the manual, or from a plug-in energy meter or smart plug. The rated figure is usually the maximum, so a meter gives a more realistic daily kWh number for anything that cycles on and off, such as a fridge or an air conditioner.
They add up. A 5 W standby load running 24 hours a day for 365 days uses 43.8 kWh, which is 8.76 at 0.20 per kWh. Replacing a 60 W bulb with a 9 W LED used 5 hours a day for 30 days cuts use from 9 kWh to 1.35 kWh, saving about 1.91 a month at 0.25 per kWh — multiply by the number of bulbs for the full effect.
The energy charge from your bill, in any currency you like, rather than the total divided by usage when there is a large fixed monthly fee. Japanese appliance catalogues often quote 31 yen per kWh as a reference: 1,500 W for 1 hour on 30 days is 45 kWh, or 1,395 yen.
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