How the estimate is calculated
Multiply watts per appliance by the quantity, daily hours, and days. Divide by 1,000 to convert watt-hours to kilowatt-hours, then multiply by the electricity rate. A 1,500-watt heater used two hours daily for 30 days consumes 90 kWh.
Rated power versus actual use
Nameplate wattage may be a maximum rather than an average. Thermostats, compressors, chargers, and variable-speed devices cycle or change load. Actual energy measured over a representative period usually gives a better estimate.
Understanding the tariff
Enter the energy price for one kWh. Utility bills may also contain fixed fees, taxes, tiered rates, time-of-use prices, demand charges, credits, or minimum charges that this calculator does not include.
Use the Power Converter when a rating is not stated in watts, and the Energy Converter for kWh and joules.
Derive a planning rate from a bill
If a bill shows 800 kWh and $136 in energy charges, an observed average energy rate is $136 ÷ 800 = $0.17 per kWh. Do not include a fixed monthly customer fee in that division if the fee would remain unchanged when the appliance is added; do include per-kWh adjustments that vary with use. For tiered or time-of-use tariffs, the next kWh may cost more or less than the bill-wide average, so use the applicable marginal period or tier when it is known.
Use scenarios for cycling appliances
A 1,500 W heater running continuously for two hours consumes 3 kWh, but a thermostat may reduce actual on-time. Compare a 25%, 50%, and 100% duty-cycle scenario instead of presenting one estimate as certain. A plug-in energy meter can supply a measured kWh value for compatible appliances; HVAC systems and fixed wiring require suitable professional methods. Keep quantity, watts, hours, days, rate, and excluded bill charges with the result so the estimate can be updated rather than rebuilt from memory.
This is a planning estimate, not a prediction of the full utility bill. Follow electrical safety instructions and do not measure circuits with unsuitable equipment.