The one formula you need
Every electricity bill comes down to kilowatt-hours (kWh): a 1,000 W appliance running for one hour uses one kWh. Rates vary a lot by state, from around 12 cents in some states to over 30 cents in California and New England, so the examples below use a typical 17 cents.
Monthly cost = (watts ÷ 1,000) × hours per day × 30 × rate per kWh.
Monthly costs at 17 cents per kWh
- Space heater (1,500 W), 4 hours a day: about $31 a month. See our space heater picks.
- Window AC (10,000 BTU inverter, about 800 W), 8 hours a night: about $33 a month. See the best window and portable ACs.
- Dehumidifier (50-pint, about 500 W), 12 hours a day in summer: about $31 a month.
- Refrigerator (ENERGY STAR, about 450 kWh a year): about $6 to $7 a month, all year.
- Ceiling or tower fan (40 W), 8 hours a day: about $1.60 a month.
Where the money goes
Anything that heats or cools is expensive: space heaters, air conditioners, dehumidifiers, clothes dryers and water heaters. Phones, routers, smart speakers and LED bulbs are small change by comparison, so do not lose sleep over chargers left plugged in.
Cheapest ways to cut the bill
- Set a smart thermostat back 7 to 10 °F for 8 hours a day; ENERGY STAR estimates savings of around 8% on heating and cooling.
- Use a fan with the AC so you can raise the thermostat a few degrees.
- Heat the room you are in with a space heater on a thermostat, not the whole house.
- Check your utility for rebates on smart thermostats, heat pumps and ENERGY STAR appliances.
- Put dehumidifiers on a humidistat at 45 to 50% rather than running them nonstop.
Buy for the bill, not just the price
A cheaper appliance with worse efficiency can cost more within two summers. On Buyrskip every product shows its usual price and key specs, so you can weigh the price tag against the running cost before you buy.
Frequently asked questions
How do I work out the running cost of an appliance?
Divide the wattage by 1,000, multiply by hours of use and by your rate per kWh. A 1,500 W heater used 4 hours a day: 1.5 × 4 × $0.17 = about $1.02 a day, roughly $31 a month.
What does ENERGY STAR save?
For appliances you run many hours, a lot. ENERGY STAR room air conditioners use about 10% less energy than standard models, and certified dehumidifiers about 15% less.
Do appliances use power on standby?
A little. TVs, game consoles, cable boxes and chargers add a few watts each; a smart plug or power strip that cuts them off saves a small but steady amount.