Electricity Cost Calculator
Enter an appliance's wattage, how many hours a day it runs, and your price per kilowatt-hour to see exactly how much it costs to run — per day, over any period, and per year — along with the kWh it consumes.
How this calculation works
Power is converted to energy first: dailyKWh = watts ÷ 1000 × hours per day. Dividing by 1000 turns watts into kilowatts, since electricity is billed per kilowatt-hour (kWh), not per watt-hour.
That daily energy use is then multiplied by your electricity rate to get a daily cost, and multiplied by the number of days you specify to get the total kWh and total cost for that period.
The yearly figure simply extends the daily cost across 365 days, assuming the appliance keeps the same daily usage pattern all year — useful for comparing appliances that run on a steady schedule.
Worked example
The formula, step by step
kWh used = watts ÷ 1000 × hours run. Multiply that by your rate per kWh to get cost. Everything else — daily, period, and yearly totals — is the same formula applied over a different number of days.
- Daily energy: watts ÷ 1000 × hours per day = kWh per day
- Period energy: kWh per day × number of days = total kWh
- Period cost: total kWh × price per kWh = total cost
- Yearly cost: daily cost × 365
Typical wattage and monthly cost for common appliances
These are rough, widely-cited figures — actual draw varies by model, size, and settings. Use your appliance's own label for an accurate number. Monthly cost assumes the listed hours per day for 30 days at 0.15 per kWh.
| Appliance | Typical power | Typical use | Est. monthly cost |
|---|---|---|---|
| Central air conditioner | 3000 W | 8 hrs/day | 108.00 |
| Refrigerator | 150 W | 24 hrs/day (cycling) | 16.20 |
| Portable space heater | 1500 W | 4 hrs/day | 27.00 |
| Desktop PC | 200 W | 6 hrs/day | 5.40 |
| LED light bulb | 9 W | 5 hrs/day | 0.20 |
Watch out for phantom loads
Devices left plugged in but switched off — TVs, chargers, game consoles, microwaves with a clock display — still draw a small trickle of power around the clock. A single phantom load might only be 1–5 watts, but a home full of them can add up to real money over a year.
To estimate a phantom load's cost, treat its standby wattage as the 'watts' input and 24 as 'hours used per day'. Unplugging idle electronics or using a switched power strip is the simplest fix.
Why wattage on the label isn't always the real draw
Some appliances list a maximum or peak wattage that the device rarely sustains — a refrigerator's compressor cycles on and off rather than running continuously, and a microwave's printed wattage is its cooking output, not its wall draw (which is usually higher). For the most realistic estimate, use a plug-in watt meter if you have one, or the appliance's average/rated wattage rather than its absolute peak.