Electricity Cost Calculator
Running cost of any appliance
Curious what an appliance costs to run? Enter its wattage, how long it runs each day and your electricity rate to see the monthly and yearly cost.
Working out running cost
Appliance energy cost comes from one figure, which is why a kwh cost calculator needs only wattage, hours and your rate.
The formula is watts ÷ 1,000 × hours × rate. A 150 W desktop running 8 hours a day at $0.16/kWh costs 1.2 kWh, or $5.84 a month and $70 a year.
Find the wattage on the label, the nameplate on the back, or in the manual. If the label gives amps instead, multiply by the voltage — 5 amps on a US 120 V circuit is 600 W. Your utility bills in kilowatt-hours, where one kWh is a 1,000 W appliance running for one hour.
What common appliances actually cost
| Appliance | Watts | Hours/day | kWh/day | Per month | Per year |
|---|---|---|---|---|---|
| LED bulb | 10 | 5 | 0.05 | $0.24 | $3 |
| Laptop | 60 | 8 | 0.48 | $2.34 | $28 |
| Desktop PC | 150 | 8 | 1.20 | $5.84 | $70 |
| Fridge (average draw) | 150 | 24 | 3.60 | $17.52 | $210 |
| Electric oven | 2,400 | 1 | 2.40 | $11.68 | $140 |
| Window air conditioner | 1,000 | 8 | 8.00 | $38.93 | $467 |
| Space heater | 1,500 | 8 | 12.00 | $58.40 | $701 |
The pattern is unmissable: anything that makes heat dominates everything else. One space heater costs more than twenty LED bulbs, a laptop and a desktop combined. Heating, cooling, water heating and tumble drying are where household electricity actually goes, and they are the only categories where changes produce visible savings.
A note on fridges
A fridge is listed at 150 W above, but it does not draw that continuously — the compressor cycles on and off, typically running 30 to 50% of the time. The 150 W figure is an average draw that already accounts for cycling, which is why it can be multiplied by 24 hours. If you enter a fridge's nameplate wattage instead, which might be 400 W, and multiply by 24, you will overstate its cost roughly threefold.
The same applies to anything thermostatically controlled: air conditioners, space heaters and water heaters all cycle. For those, either use an average draw across the day or enter the nameplate wattage with the hours it is actually running, not the hours it is switched on.
Standby power, in proportion
"Vampire" loads are real but routinely overstated. A device drawing 2 W on standby costs about $2.80 a year. Twenty of them is $56 — worth addressing, and still less than a single space heater running through one winter month.
- Worth unplugging: older set-top boxes and games consoles in non-eco modes, which can draw 15 to 20 W idle.
- Barely worth it: phone chargers with nothing attached, at well under a watt.
- Do not unplug: anything that needs to stay on, and never a fridge to save standby power.
Spending an evening chasing standby loads while an electric water heater runs at default settings is optimising the wrong end of the bill.
Making the number accurate
- Check your actual rate. The US average is around $0.16/kWh but state averages run from roughly $0.11 to over $0.40, and many bills add fixed supply charges on top of the per-kWh rate.
- Watch for time-of-use pricing. If your tariff varies by hour, running a dryer at peak can cost two or three times the off-peak figure.
- Measure rather than guess where it matters. A plug-in energy monitor costs very little and settles arguments about what a specific appliance really draws.
- Nameplate wattage is a maximum, not a typical draw. Most devices use less than the label most of the time.
Sizing solar against your usage? The solar payback calculator works from your monthly bill, and the EV charging calculator covers what a car adds.
How this electricity cost calculator works out its numbers
Energy is watts ÷ 1,000 × hours per day, giving kWh per day. Cost multiplies that by your rate. Monthly figures use 30.44 days (365 ÷ 12), so the monthly result times 12 equals the annual one exactly.
- Constant draw is assumed. Thermostatically controlled appliances cycle, so enter an average draw across the day rather than nameplate wattage, or nameplate wattage with the hours it actually runs.
- Nameplate wattage is a maximum, not typical consumption. Most devices draw less than the label most of the time.
- Flat rate assumed. Time-of-use tariffs, tiered pricing and fixed monthly supply charges are not modelled, and all three appear on real bills.
- Appliance figures in the table are typical values for illustration; actual wattage varies considerably by model and age.
- Not included: standby draw when the device is off, power factor for inductive loads, and any efficiency losses upstream of the socket.
Reviewed September 2026.
Figures reviewed . Every worked example on this page is checked against the calculator above.
Electricity Cost Calculator: frequently asked questions
How do I calculate appliance running cost?
Divide watts by 1,000, multiply by hours used per day, then by your rate per kWh. A 150 W device for 8 hours at $0.16 is 1.2 kWh, about $5.84 a month.
What uses the most electricity at home?
Anything that makes heat: space heating, air conditioning, water heaters and tumble dryers, plus anything running constantly like a fridge. A single space heater at 8 hours a day costs about $701 a year at $0.16/kWh.
How do I convert amps to watts?
Multiply amps by volts. A device drawing 5 amps on a 120-volt US circuit uses about 600 watts. Then divide by 1,000 for kilowatts and multiply by hours and your rate.
Why does my fridge use less than its nameplate says?
Because the compressor cycles on and off, typically running 30 to 50% of the time. Use an average draw of around 150 W over 24 hours rather than the nameplate figure, which would overstate the cost roughly threefold.
How much does standby power really cost?
About $2.80 a year per watt of standby draw. Twenty devices at 2 W each is $56 a year — worth addressing but far less than one space heater used through a single winter month.
How much does it cost to run a space heater?
A 1,500 W heater for 8 hours a day is 12 kWh, about $58 a month or $701 a year at $0.16/kWh. Electric resistance heating is the most expensive way to heat a room.
What is a kilowatt-hour?
The energy used by a 1,000-watt appliance running for one hour. It is the unit your utility bills in, so every appliance cost calculation converts to kWh before applying the rate.
What is the average cost of electricity?
Around $0.16 per kWh across the US, but state averages range from roughly $0.11 to over $0.40. Check a recent bill, and note many utilities add a fixed monthly supply charge on top of the per-kWh rate.