How to Calculate Electricity Costs (kWh)
Your electricity bill is measured in kilowatt-hours (kWh). Once you can turn an appliance's wattage and running time into kWh, you can cost anything in your home — and spot where the real money goes.
What a kilowatt-hour is
A kilowatt-hour is one kilowatt (1,000 watts) of power used for one hour. A 1,000-watt heater run for an hour uses 1 kWh; a 100-watt device run for 10 hours also uses 1 kWh. Your utility charges a set price per kWh, so cost is simply energy used times that rate.
The formula
Cost = power (kW) x hours used x price per kWh. A 1.5 kW air conditioner run 6 hours a day at $0.20 per kWh costs 1.5 x 6 x 0.20 = $1.80 a day, about $54 a month. The Electricity Cost Calculator does this for any appliance and rate — just read the wattage off its label.
Where the savings really are
Big savings come from high-wattage or always-on devices, not from unplugging small ones. Heating, cooling, water heaters and old lighting dominate bills. Swapping a single 60-watt incandescent bulb for a 9-watt LED that gives the same light cuts that bulb's running cost by roughly 85% — multiplied across a whole house, it adds up fast.
Reading your bill
Your bill shows total kWh used and the price per kWh, sometimes split into tiers or time-of-use rates. If a rate is higher at peak hours, shifting heavy use — laundry, dishwasher — to off-peak times lowers the cost without using any less energy overall.
Frequently asked questions
Where do I find an appliance's wattage? On a label on the device or in its manual; if only amps are listed, multiply amps by volts to get watts.
Does standby power matter? A little — idle devices sip a few watts each, which adds up across many, but it is minor next to heating and cooling.
Why is my bill higher in summer or winter? Air conditioning and heating are among the highest-wattage things most homes run, and they run for hours.
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Last updated: August 27, 2026