Enter watts, hours per day, your price per kilowatt-hour, and how many days to total. The result is watt-hours converted to kilowatt-hours, then multiplied by your rate.
| LED bulb | 9 | 2.16 kWh | $0.35 |
| Router | 12 | 2.88 kWh | $0.46 |
| Space heater | 1500 | 360 kWh | $57.60 |
A 60 watt device run 8 hours uses 0.48 kilowatt-hours that day. Over 30 days that is 14.4 kilowatt-hours. At 16 cents each, the energy is about $2.30. Heaters and clothes dryers dominate this math because their wattage is high, not because they are on all day.