How it's calculated
cost = (watts ÷ 1,000) × hours/day × days × rate
watts = device power, hours/day = daily run time, days = period length, rate = electricity price per kWh. Energy used (kWh) = (watts ÷ 1,000) × hours.
Worked examples
| Appliance | Watts | Hours/day | Cost/month (15¢/kWh) |
|---|---|---|---|
| Space heater | 1500 | 8 | $54.00 |
| Refrigerator | 150 | 24 | $16.20 |
| LED TV | 100 | 5 | $2.25 |
Common questions
How do I find an appliance's wattage?
Check the label on the back or bottom, or look it up in the manual. If only amps and volts are listed, multiply them to get watts.
What electricity rate should I use?
Pick your state for the EIA average, or enter the per-kWh rate from your own utility bill for the most accurate result.