PlenumHubThe formula
Electricity is billed in kilowatt-hours (kWh): one kWh is one kilowatt (1,000 watts) of power used for one hour. To find an appliance's energy use: kWh = (watts ÷ 1000) × hours used. To find the cost: cost = kWh × your price per kWh.
For example, a 1,500 W space heater run for 3 hours a day: kWh per day = (1500 ÷ 1000) × 3 = 4.5 kWh. At $0.18 per kWh, that's 4.5 × 0.18 = $0.81 per day, or about $24.30 over a 30-day month.
Typical wattage of common appliances
| Appliance | Typical wattage |
|---|---|
| Refrigerator | 100-400 W (cycles on and off; averages to roughly 1-2 kWh/day) |
| Air conditioning unit (window/portable) | 900-1,500 W |
| Space heater | 750-1,500 W |
| LED light bulb | 5-15 W |
| Washing machine | 350-1,200 W (varies a lot by cycle, mostly for heating water) |
These are rough ranges. Actual wattage varies a lot by model, size and settings, so treat this table as a starting point, not a substitute for your specific appliance's rating.
Finding your appliance's actual wattage
The most reliable source is the rating label, usually on the back, bottom or inside of the appliance, or in its manual, which lists watts (W) directly. If it only lists amps (A) and volts (V), multiply them together to estimate watts (amps × volts = watts). For the most accurate real-world figure, a plug-in electricity usage monitor measures actual power draw, which is especially useful for appliances like fridges and washing machines whose power use varies a lot during a cycle rather than staying constant.
Limits of this estimate
This calculator assumes constant wattage for the hours you enter, which is accurate for simple resistive devices like heaters and incandescent bulbs, but only an approximation for appliances that cycle on and off (fridges, air conditioners) or draw different power at different stages (washing machines, dishwashers). It also doesn't include standby ("phantom") power draw when a device is plugged in but switched off. For those appliances, a plug-in usage monitor over a few days will give a more accurate average than the wattage on the label alone.
Frequently asked questions
Where do I find my price per kWh?
Check a recent electricity bill, which usually lists a rate per kWh (or per unit). Your utility provider's website or customer service can also give you the current rate.
Does this work outside the US?
Yes. Enter your price per kWh in your own currency and the result will be in that same currency; the calculator doesn't assume dollars.
Why doesn't the fridge/AC cost match the table exactly?
Fridges, air conditioners and similar appliances cycle on and off rather than drawing constant power, so their average wattage over a day is lower than their rated (peak) wattage. Use a plug-in usage monitor for a more accurate figure.
What if I enter 0 hours per day?
The calculator will show $0 and 0 kWh, since an appliance that isn't used doesn't consume energy in this model. This doesn't account for standby power draw.