Electric BillsWhat Is a Kilowatt-Hour (kWh)? How to Calculate Electricity Cost
A kilowatt-hour is 1,000 watts used for one hour. Here's how kWh differs from kW and how to calculate what any appliance costs to run.
Free electricity calculators
Work out electricity costs, monthly bills, appliance running costs, kWh, amps, solar payback and EV charging – with every state's latest average rate built in.
- Electricity cost calculatorTurn kWh into dollars at your state's rate.
- Electric bill calculatorEstimate a monthly bill from your usage.
- Appliance energy cost calculatorWatts and hours to cost per day, month and year.
- kWh calculatorConvert watts and hours into kWh – and cost.
- Watts to amps calculatorConvert watts ↔ amps at 120 V, 240 V or any voltage.
- Solar panel calculatorSystem size, cost, savings and payback.
- EV charging cost calculatorHome charging cost per month and per mile.
Which calculator do I need?
- Know your kWh? Use the electricity cost calculator to turn it into dollars, or the electric bill calculator for a full monthly bill.
- Know the watts? The appliance energy cost calculator gives cost per day, month and year; the kWh calculator converts watts and hours into kWh.
- Sizing a circuit? The watts to amps calculator converts at 120 V, 240 V or any voltage.
- Thinking about solar or an EV? Try the solar panel calculator and the EV charging cost calculator.
The formulas behind them
- kWh = watts × hours ÷ 1,000
- Cost = kWh × rate (¢/kWh) ÷ 100
- Amps = watts ÷ volts (DC and resistive loads)
Rates are built in for every state: the US 12-month average is 18.16¢ per kWh, from 12.35¢ in North Dakota to 44.27¢ in Hawaii (EIA, through August 2026).
Frequently asked questions
Are these electricity calculators free?
Yes. All calculators are free, need no sign-up and run in your browser.
Where do the electricity rates come from?
Each state's 12-month average residential rate from the U.S. Energy Information Administration (Form EIA-861M). You can also type in the rate from your own bill.
How accurate are the results?
The maths is exact; accuracy depends on your inputs. Use your appliance's actual wattage and the rate on your bill, and remember thermostats and compressors cycle on and off.
What is the difference between kW and kWh?
kW is power – how fast electricity is used at a moment. kWh is energy – power used over time. A 2 kW heater running for 3 hours uses 6 kWh.
How many amps is 1,500 watts at 120 volts?
1,500 W ÷ 120 V = 12.5 amps.
Guides that use these tools
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Practical ways to lower your electric bill, from free thermostat and standby-power fixes to LEDs, insulation and rate plans, each backed by DOE, EPA or EIA guidance.
Electric VehiclesHow Much Does It Cost to Charge an Electric Car at Home?
Home EV charging cost comes down to your car's kWh per 100 miles, your miles driven and your electricity rate. Here is the simple formula with a worked example.