How this calculator works
Pick an appliance from the list or type its wattage, enter how many hours a day you use it and your price per kWh, and you’ll get its cost per day, month and year and how many kWh it uses. The appliances on the list fill in typical values you can adjust.
The formula
kWh = watts × hours ÷ 1,000 and cost = kWh × price per kWh
A 1,500-watt space heater running 4 hours a day uses 6 kWh a day. At $0.17 per kWh that’s $1.02 a day, $30.60 a month and $367 a year.
What you pay per kWh
The US average for homes is roughly 17 cents per kWh, but it varies enormously by state: from around 11 cents in the cheapest states to over 40 cents in Hawaii. For the real number, divide the total on your latest bill by the kWh you used; that includes delivery charges and taxes, which the price per kWh on the rate sheet often doesn’t.
What common appliances cost
At $0.17 per kWh:
| Appliance | Use | Per month |
|---|---|---|
| Electric water heater (4,500 W) | 3 h a day | $68.85 |
| Window air conditioner (1,200 W) | 8 h a day | $48.96 |
| Space heater (1,500 W) | 4 h a day | $30.60 |
| Electric dryer (5,000 W) | 12 loads a month | $10.20 |
| Refrigerator (150 W) | 8 h of running a day | $6.12 |
| Wi-Fi router (10 W) | Always on | $1.22 |
| LED bulb (9 W) | 5 h a day | $0.23 |
The pattern is clear: anything that makes heat or cold dominates the bill. Swapping a 60-watt incandescent bulb for a 9-watt LED saves about $1.30 a month per bulb, which adds up across a house but is small next to the water heater.
Reading the label correctly
The wattage on the label is the maximum the appliance draws. Some run flat out whenever they’re on, like a space heater, a kettle or a hair dryer. Others cycle: a refrigerator’s compressor runs only part of the time, which is why the calculator assumes about 8 hours a day rather than 24. For those, a plug-in energy meter tells you the real consumption over a few days.
Standby power
Devices that are “off” but plugged in, like TVs, game consoles and chargers, keep drawing a few watts. Each one is tiny, but a house full of them can add up to 5% to 10% of the bill. A power strip you switch off at night takes care of most of it.
If you’re weighing an electric car, the gas cost calculator compares charging at home with filling up.