How this number is made
Electricity is sold in kilowatt-hours: a thousand watts running for one hour. A space heater at 1,500 watts uses 1.5 kWh every hour it is on. Multiply by your rate. The rate is on the bill, often between the energy charge and a pile of fixed fees this page does not invent.
- For a whole month, use the kWh line on the bill and the energy rate, not the total due divided by nothing.
- For one device, use the watts on the label. A “1,500 W” heater is 1.5 kW.
- Type the rate in your currency. Sixteen cents is 0.16, not 16.
Formula
kWh = (watts ÷ 1,000) × hours per day × days. Cost = kWh × price per kWh.
Worked example
A 1,500-watt heater for one hour a day over 30 days uses 45 kWh. At $0.16 per kWh that is $7.20. Leave it on for eight hours and it is $57.60, before fees.
Questions
Why is my bill higher than this?
Utilities charge a customer charge, fuel adjustments, taxes, and sometimes a different rate above a usage tier. This page is the energy line, which is the part you can change by using less.
Do LED bulbs matter next to heat and cooling?
A 10-watt bulb is cheap even if you forget it. Heat, air conditioning, water heating, and clothes drying dominate most bills. Run those through the appliance mode before you optimize lamps.