Appliance & electricity bill cost — methodology

What this calculator does

It turns an appliance’s power draw and how often you use it into energy (kilowatt-hours) and money — per day, per month and per year — at the electricity price you enter. It also places your appliance next to a few representative typical household loads so you can judge whether it is big or small.

The formulas

Energy and cost

daily_kwh   = (power_watts / 1000) * hours_per_day * (days_per_week / 7) * quantity
annual_kwh  = daily_kwh * 365
annual_cost = annual_kwh * price_per_kwh
monthly_cost = annual_cost / 12
daily_cost  = daily_kwh * price_per_kwh

We convert watts to kilowatts (÷ 1,000), multiply by the hours it runs, and scale by the fraction of the week it is used (days_per_week / 7) so that a device used only some days is averaged correctly across the year. Multiplying by quantity covers several identical units.

Comparison appliances

comparison_cost = comparison_annual_kwh * price_per_kwh

The comparison bars use a fixed preset of representative typical annual figures (LED bulb ~30 kWh, laptop ~60, refrigerator ~400, desktop PC ~600, clothes dryer ~900, window AC ~1,000, electric water heater ~3,500), each costed at your price. These are illustrative typical values for context, not measurements of your own appliances.

Default values

The electricity price defaults to a US residential average and is editable in the calculator and shown with its source in the calculator’s assumptions table. It is the most time-sensitive input — always replace it with your own rate from a recent bill. The power, hours, days and quantity are appliance-specific inputs you supply.

How we keep it honest

The calculation logic lives in a small, pure function that is unit-tested against normal, edge and invalid inputs (for example, a non-finite wattage returns “no result” rather than a misleading number). If you spot an error, tell us and we’ll fix it.