How this calculator works
Energy in kilowatt-hours is watts × hours ÷ 1,000. Multiply by your price per kWh to get cost. Appliances that cycle on and off (fridges, AC) use less than their rated watts on average, so a plug-in energy meter gives the most accurate number.
kWh per day = Watts × Hours ÷ 1000
Monthly cost = kWh per day × Days × Rate
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Power use | 1,000 W |
| Hours used per day | 3 h |
| Days used per month | 30 |
| Electricity rate | 0.182 $/kWh |
| Result | Value |
|---|---|
| Cost per month | $16.38 |
| Cost per year | $196.56 |
| Cost per day of use | $0.55 |
| Energy per month | 90 kWh |
| Energy per year | 1,080 kWh |
Step by step:
- kWh per day = 1,000 × 3 ÷ 1000 = 3
- Per month = 3 × 30 = 90 kWh
- Cost = 90 × $0.182 = $16.38
Monthly cost of common appliances
At 18.2¢/kWh, 30 days.
| Appliance & daily use | Cost per month | Energy per month |
|---|---|---|
| Space heater 1,500 W, 8 h | $65.52 | 360 kWh |
| Window AC 1,000 W, 8 h | $43.68 | 240 kWh |
| Gaming PC 400 W, 4 h | $8.74 | 48 kWh |
| Refrigerator avg 150 W, 24 h | $19.66 | 108 kWh |
| LED TV 100 W, 5 h | $2.73 | 15 kWh |
Common mistakes to avoid
- Using maximum label watts for appliances that cycle (fridges, AC) — measure with a plug-in meter.
Frequently asked questions
How much does it cost to run a 1,500 W space heater?
At 18.2¢/kWh, 1.5 kW for 8 hours uses 12 kWh — about $2.18 a day.
Where do I find an appliance’s watts?
On its label or nameplate, or in the manual. If only amps are listed, watts ≈ volts × amps.