Free electricity cost calculator
See exactly what any appliance costs to run by the day, month, and year from its wattage and your rate — updated live, as you type.
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US average ~$0.13/kWh. Find your exact rate on your monthly utility bill.
Results are estimates. Consult a professional.
How the electricity cost calculator works
Your power company does not bill you for watts — it bills you for energy used over time, measured in kilowatt-hours (kWh). This electricity cost calculator turns a device's wattage and how long you run it into energy, then multiplies by the price you pay per kilowatt-hour to show the cost per day, per month, and per year at once. Enter the power rating from the label, your daily hours of use, and your rate, and the numbers update as you type.
How electricity is billed: the kilowatt-hour
A kilowatt-hour is the amount of energy used by a 1000-watt load running for one hour. It is the single unit on your bill that costs money. The same kilowatt-hour can come from many shapes of use — and they all cost the same.
- A 1000 W space heater for 1 hour = 1 kWh.
- A 100 W bulb for 10 hours = 1 kWh.
- A 2000 W kettle for 30 minutes = 1 kWh.
The electricity cost formula explained
Three inputs drive the result, and each pulls the cost in a straight line — double any one of them and the cost doubles.
Watts — the power rating
The wattage is printed on the appliance label, the nameplate, or the charger. A label that lists volts and amps instead gives you watts by multiplying them: 120 V × 5 A = 600 W. Motors, heaters, and air conditioners draw the most; LED bulbs, phone chargers, and standby electronics draw the least.
Hours per day — the run-time
Use the realistic average, not the maximum. A fridge cycles its compressor on and off, so it runs at full wattage only a third of the time; entering the equivalent run-hours, rather than 24, keeps the estimate honest. Heating and cooling are seasonal, so an annual figure built from a peak-summer hour count will overstate the year.
Rate — the price per kilowatt-hour
This is the number that varies most between households. It is the "energy charge" on your bill in dollars per kWh. Many bills also carry fixed delivery and service fees that this rate does not include, so your total bill is always a little higher than wattage maths alone.
A worked example using the electricity cost calculator
Dana leaves a 100 W game console and TV setup on for about 5 hours every evening. Her utility charges $0.15 per kWh. She wants to know what that habit costs over a day, a month, and a year.
Step 1 — Find the daily energy in kWh
kWh per day = (100 W × 5 h) ÷ 1000 = 0.5 kWh. That is half a kilowatt-hour each evening.
Step 2 — Multiply by the rate
Cost per day = 0.5 kWh × $0.15 = $0.075, about seven and a half cents a day.
Step 3 — Scale up to a month and a year
Over an average month (30.44 days): 0.5 × 30.44 = 15.22 kWh, costing $2.28. Over a year (365.25 days): 0.5 × 365.25 = 182.6 kWh, costing $27.39.
Appliance wattage and running-cost reference table
Typical power ratings for common household appliances, with a rough yearly running cost at $0.15/kWh and the everyday usage shown. Your own wattage and hours will differ — check the label — but these give a sense of which devices dominate a bill.
| Appliance | Typical wattage | Assumed daily use | ~ Cost / year |
|---|---|---|---|
| LED light bulb | 10 W | 5 h | $3 |
| Laptop | 50 W | 6 h | $16 |
| Refrigerator | 150 W | 8 h (cycling) | $66 |
| Desktop PC | 200 W | 4 h | $44 |
| Clothes dryer | 3000 W | 1 h | $164 |
| Dishwasher | 1800 W | 1 h | $99 |
| Space heater | 1500 W | 4 h | $329 |
| Window AC unit | 1000 W | 8 h | $438 |
| Central air conditioning | 3000 W | 6 h | $986 |
Costs computed from kWh/year = watts × hours/day ÷ 1000 × 365.25, at $0.15/kWh, rounded to whole dollars. Heating, cooling, and the dryer are the heavy hitters; lights and electronics are minor by comparison.
For the electrical side of these loads — sizing wire so it does not overheat, or checking how much voltage a long run loses — see the voltage drop calculator, and use Ohm's law to convert between volts, amps, and watts.
Watts vs volt-amps (and why your bill counts watts)
Multiplying volts by amps gives volt-amps (VA), the apparent power. For a simple resistive load like a heater or an incandescent bulb, volt-amps equal watts. But for motors, transformers, and many power supplies, the current and voltage fall out of step, so the real power in watts is lower than the volt-amp figure. The ratio between them is the power factor.
Standby and phantom load: the always-on cost
Many devices keep drawing power when they look off — a TV waiting for the remote, a charger left plugged in, a game console in rest mode, a microwave clock. This standby draw, often called phantom or vampire load, is usually 1 to 10 watts per device, but it runs 24 hours a day, every day.
A single 5 W standby load left on all year uses 5 × 24 ÷ 1000 × 365.25 = 43.8 kWh, about $6.57 at $0.15/kWh. Across a whole home, the US Department of Energy estimates these always-on loads add up to roughly 5 to 10 percent of a household's electricity bill.
The US Department of Energy's Energy Saver guidance describes "energy vampires" and recommends smart power strips and unplugging idle electronics to cut standby waste.How to cut your electricity bill
Because cost is wattage times hours times rate, you have three levers: lower the wattage, cut the hours, or pay a lower rate. The biggest savings come from the heating, cooling, and large-appliance loads at the top of the reference table — not from switching off a phone charger.
- Attack the big loads first. Heating and cooling typically dominate a bill; a one-degree thermostat change saves more than unplugging every gadget in the house.
- Cut run-time, not just wattage. A device used fewer hours saves money even at the same rating — timers, motion sensors, and habit changes all reduce hours.
- Swap to lower-wattage equipment. An LED bulb (about 10 W) does the job of a 60 W incandescent; heat-pump heating and cooling beats resistive heaters.
- Kill standby waste. Smart power strips and unplugging idle electronics remove the always-on phantom load.
- Shift use to cheaper hours. If you are on a time-of-use plan, running the dishwasher or charging overnight can cut the rate you pay for those kilowatt-hours.
Where to find your electricity rate
The most important input is your real price per kilowatt-hour, and the surest place to find it is your own electricity bill rather than a national average.
- Look on your bill for "$/kWh", "rate", "price per kWh", or "energy charge".
- If your bill lists tiers or time-of-use blocks, use the rate for the block you actually use most.
- To approximate from the total: divide the total energy charge by the kWh used that period.
- No bill handy? Your utility's website lists current residential rates, and the EIA publishes state averages.
Frequently asked questions about the free electricity cost calculator
About this electricity cost calculator
This electricity cost calculator runs entirely in your browser — nothing is sent anywhere. Enter a device's wattage, the hours you run it each day, and your price per kilowatt-hour, and it converts watts and time into kilowatt-hours, then multiplies by your rate to show the cost per day, per month, and per year at once. Use it to compare appliances, size up a standby load, or sanity-check a line on your utility bill.