THE BIG USERS
Appliance Electricity Use: Watts, kWh & Running Costs
BillMellow editorial · Updated October 25, 2026
Power and time work together. A high-power device used briefly may consume less energy than a lower-power device left on all day.
Watts are a rate. kWh is energy.
1,000 watts for one hour is 1 kWh. At an illustrative $0.18/kWh, a 1,500-watt heater operated continuously for four hours uses 6 kWh and costs $1.08 in energy charges.
Measure cycling appliances
Refrigerators and air conditioners cycle and may vary their output. Multiplying nameplate watts by 24 hours can give a misleading estimate. Use measured kWh, an appropriate energy label or average operating power when available.
Start with your actual routine
Use the whole-home calculator to compare devices with your own inputs. The result describes the appliances you add; it is not a prediction of every line on your utility bill.
Source: US Energy Information Administration: measuring electricity
How to calculate appliance electricity cost
For a device with a known average operating power, daily energy use is watts ÷ 1,000 × operating hours. Multiply the resulting kWh by your variable electricity rate. Multiply daily cost by the days used for a monthly estimate. The annual result assumes that daily routine repeats for 365 days.
Space heater example
A 1,500-watt heater operating at that power for four hours uses 1.5 × 4 = 6 kWh. At an illustrative $0.18 per kWh, the energy cost is $1.08 per day and $32.40 over 30 days. This is not a US average or a quote from a utility. If a thermostat switches the heater off part of the time, four elapsed hours may be different from four full-power operating hours.
Where to find the right inputs
- Power: check the device label or manual. Rated maximum power is not always typical operating power.
- Operating time: use the time the device draws the entered power. Convert 30 minutes to 0.5 hours.
- Energy measurement: for a cycling device, measured kWh over a representative period can be more useful than rated watts × elapsed time.
- Rate: include the variable per-kWh charges relevant to that use. Keep fixed monthly fees separate.
Does a lower-wattage appliance cost less?
It draws less power while operating at that level, but it may need to run longer or provide a different level of service. Compare equivalent performance and annual energy use before calling a replacement more efficient. In our replacement example, reducing annual use from 1,000 to 600 kWh at $0.18 saves $72 a year. A $300 purchase takes about 4.2 years to recover through energy savings alone.
Calculate appliance running costs or compare replacement cost and simple payback. These calculations exclude maintenance, financing, rebates and future rate changes.