How to use the electricity cost calculator
- Enter the appliance's power in watts, from its label or manual.
- Enter the hours it runs per day and the days per year you use it.
- Enter your electricity rate per kWh from your bill. The $0.15 default is only an example.
Use the rate printed on your latest bill rather than a national average; Decoratoradvice has seen rates vary widely between states and plans.
Electricity cost formulas
kWh per day = watts × hours per day ÷ 1,000
kWh per year = kWh per day × days used per year
Cost per year = kWh per year × rate
Average per month = cost per year ÷ 12
Worked examples
A 1,000 W space heater used 3 hours a day, every day, at $0.15 per kWh:
1,000 × 3 ÷ 1,000 = 3 kWh per day
3 × 365 = 1,095 kWh per year
1,095 × $0.15 = $164.25 per year, about $13.69 a month
A device drawing 150 W around the clock:
150 × 24 ÷ 1,000 = 3.6 kWh per day
3.6 × 365 = 1,314 kWh = $197.10 per year at $0.15
Finding your rate
Your bill shows your actual price per kWh, sometimes split into supply and delivery charges; add them. For a state comparison, the U.S. Energy Information Administration's state electricity profiles list the average retail price in each state.
Tips
- Appliances that cycle, such as refrigerators and air conditioners, do not draw full power all the time. A plug-in watt meter gives the real figure.
- For room air conditioners, size first with the BTU calculator, then use the unit's wattage here.
- Compare an upgrade's yearly saving with its cost in the energy upgrade payback calculator.
- For outage planning, the same wattage feeds the generator size calculator.
Common mistakes
- Using the maximum wattage for cycling appliances. Measure or use the annual kWh from the EnergyGuide label.
- Forgetting standby power for devices that are always plugged in.
- Using a rate without delivery charges. Add all per-kWh charges from your bill.
Frequently asked questions
How do I calculate kWh?
Watts × hours ÷ 1,000. A 100 W bulb on for 10 hours uses 1 kWh.
How much does it cost to run a 1,500 W heater?
At $0.15 per kWh, 1.5 kWh per hour costs about $0.23 an hour.
What is a kilowatt-hour?
The energy used by a 1,000 W appliance running for one hour.
Where do I find an appliance's wattage?
On the nameplate, in the manual, or by measuring with a plug-in watt meter. If only amps are listed, multiply by the voltage.
How much does lighting cost to run?
Enter a bulb's wattage and hours. Plan how many bulbs a room needs with the room lighting calculator.
Does a water heater use a lot of electricity?
Electric water heaters are among the larger household loads. Size one with the water heater size calculator.
Key takeaways
- kWh = watts × hours ÷ 1,000.
- Cost = kWh × your full per-kWh rate.
- Measure cycling appliances rather than using peak watts.
- Use your own bill for the rate.