Electricity Cost Calculator
An electricity cost calculator uses watts × hours ÷ 1,000 = kWh, then kWh × rate. A 1,000 W device run 5 h a day at $0.15/kWh costs $0.75 a day or $274 a year.
How much does it cost to run an appliance?
An electricity cost calculator converts power into energy, then energy into money. Kilowatt-hours per day = watts × hours per day ÷ 1,000, and cost = kWh × your rate per kWh. A 1,000 W device run 5 hours a day uses 5 kWh. At $0.15 per kWh, that is $0.75 a day, $22.50 over 30 days, and $273.75 over a year. The calculator shows the month and year rounded to the dollar: $23 and $274.
Watts are how hard a device pulls at any moment, and hours are how long it pulls. Your bill charges for the two multiplied together.
The formula in plain words
- Watt-hours per day = watts × hours used per day.
- kWh per day = watt-hours ÷ 1,000.
- Cost per day = kWh × rate.
- Cost per month = cost per day × 30.
- Cost per year = cost per day × 365.
Doubling either the wattage or the hours doubles the cost.
Worked examples
- A 1,000 W device, 5 hours a day, $0.15/kWh (calculator defaults)
- Energy: 1,000 × 5 ÷ 1,000 = 5.00 kWh per day
- Per day: 5 × $0.15 = $0.75
- Per month: $0.75 × 30 = $22.50, shown as $23
- Per year: $0.75 × 365 = $273.75, shown as $274
- A 1,500 W space heater, 6 hours a day, $0.16/kWh
- Energy: 1,500 × 6 ÷ 1,000 = 9.00 kWh per day
- Per day: 9 × $0.16 = $1.44
- Per month: $1.44 × 30 = $43.20, shown as $43
- Per year: $1.44 × 365 = $525.60, shown as $526
1,500 W is the usual top setting on a plug-in heater. If its thermostat cycles it off half the time, the real cost is about half, since it only draws power while the element is on.
Monthly cost by wattage at $0.15/kWh
| Device wattage | 4 h/day: kWh per day | 4 h/day: per month | 24 h/day: per month | 24 h/day: per year |
|---|---|---|---|---|
| 10 W | 0.04 | $0.18 | $1.08 | $13.14 |
| 100 W | 0.40 | $1.80 | $10.80 | $131.40 |
| 500 W | 2.00 | $9.00 | $54.00 | $657.00 |
| 1,000 W | 4.00 | $18.00 | $108.00 | $1,314.00 |
| 1,500 W | 6.00 | $27.00 | $162.00 | $1,971.00 |
| 3,000 W | 12.00 | $54.00 | $324.00 | $3,942.00 |
At a different rate, scale the dollars. At $0.30 per kWh, every cost in the table doubles.
How to find the inputs
- Watts: read the nameplate sticker or the manual. If it lists amps and volts only, multiply them: 10 A × 120 V = 1,200 W. The amps to watts calculator does this, including power factor.
- Hours per day: be honest. A TV left on in the background counts.
- Rate: divide your last bill’s total by the kWh it shows. That captures fees and taxes.
- Cycling devices: use a plug-in energy meter for a few days and enter its average kWh per day as hours × watts.
Common mistakes
- Using the nameplate for a cycling appliance. It overstates the cost of fridges, freezers, and thermostat-controlled heaters.
- Forgetting the 1,000. Watts × hours × rate without dividing gives a cost 1,000 times too high.
- Using only the energy charge. The per-kWh line on a bill can leave out delivery charges, which may be billed per kWh too.
- Mixing up kW and kWh. kW is how hard a device pulls; kWh is how much energy it used over time.
Using the result
Add up the kWh per day of your main loads to size a backup system with the generator size calculator or a solar array with the solar panel calculator. For heating, the heat pump vs gas furnace calculator compares running costs over a whole season. New circuits for big loads should be sized and installed by a licensed electrician under your local code.
Frequently asked questions
How is the running cost of an appliance calculated?
Multiply watts by hours used per day and divide by 1,000 to get kilowatt-hours (kWh). Multiply kWh by your rate for the daily cost, then by 30 for a month and 365 for a year. A 1,000 W device run 5 hours a day uses 5 kWh, which is $0.75 a day at $0.15 per kWh.
Where do I find my electricity rate?
On your utility bill. The simplest rate to use is the total bill divided by the kWh used that month, which folds in delivery charges and taxes. A $96 bill for 600 kWh is $0.16 per kWh. Time-of-use and tiered plans make the real rate vary by hour or season.
Why divide the wattage by 1000?
Utilities bill in kilowatt-hours, and a kilowatt is 1,000 watts. A 100 W bulb on for 10 hours uses 1,000 watt-hours, which is 1 kWh. Dividing by 1,000 turns watt-hours into the unit on your bill.
Why is my real cost lower than the label wattage suggests?
Many appliances cycle. A refrigerator, heater, or air conditioner with a thermostat runs its compressor or element only part of the time, so its average draw is well below the nameplate. For those, a plug-in energy meter over a few days gives the true kWh per day.
Does this include standby or phantom power?
Only if you include it. The calculator assumes the device draws its full wattage for the hours you enter. For an always-on standby load, enter its small wattage and 24 hours: a 5 W standby draw costs 5 × 24 ÷ 1,000 × $0.15 = $0.018 a day, about $6.57 a year.
Estimates only. Verify quantities with your supplier before purchasing.