Electric Bill & Appliance Wattage Cost Calculator

From wattage and usage hours to an actual dollar cost

A 1,200-watt appliance running 1.5 hours per day for 30 days uses 54.00 kWh total, costing $8.64 at $0.16 per kWh -- an average of $0.288 per day.

The core conversion is watts to kilowatt-hours: 1,200 watts x 1.5 hours = 1,800 watt-hours per day, divided by 1,000 to get 1.8 kWh/day, multiplied by 30 days = 54 kWh total -- the watt-to-kilowatt-hour conversion (dividing by 1,000) is the step most often missed when estimating appliance cost by hand.

At 30 days of 1.5 hours daily use, this appliance is only actually drawing power for 45 total hours out of the full 720 hours in a 30-day month -- most household appliances used intermittently like this represent a fairly small fraction of total possible runtime, which is exactly why per-appliance costs like this one are usually modest individually even for a fairly power-hungry device.

Why nameplate wattage isn't the whole story

Nameplate watts, not a smart-plug measurement. Standby draw is omitted. The wattage entered here is typically the nameplate rating (printed on the appliance or its manual) -- many appliances' actual power draw varies during operation (a heating element cycling on and off, a motor under variable load) rather than pulling a perfectly constant wattage the whole time it's 'on,' so a smart plug's real measured usage can differ from a calculation based on the nameplate figure alone.

Standby power draw -- the small amount of electricity many electronics and appliances consume even when nominally 'off' but still plugged in -- isn't included in this calculation at all, which only counts the hours the appliance is actively in its specified running mode.

For appliances with genuinely variable power draw (a refrigerator cycling its compressor, for example, rather than running continuously at a fixed wattage), this calculator's constant-wattage assumption is a rougher approximation than it would be for something with a truly steady draw, like an incandescent bulb or a space heater on a fixed setting.

Getting a more accurate real-world number

A smart plug or dedicated energy monitor that measures actual real-time power draw over time gives a more accurate picture than nameplate wattage alone, especially for appliances with variable draw or meaningful standby consumption.

For a related energy-cost calculation using the same rate-times-usage structure, but for EV charging instead of a household appliance, the EV Charging Time & Cost Estimator applies similar math.

Frequently Asked Questions (FAQ)