References and Methodology

Core formula

Every appliance calculator starts with the same electricity cost formula. Watts are converted to kilowatts, then multiplied by runtime and electricity rate.

Cost = Watts / 1000 x Hours Used x Electricity Rate

The same conversion is used for energy consumption:

kWh = Watts / 1000 x Hours Used

Wattage ranges

Wattage ranges on WattCostGuide are planning estimates for common household appliances. They are intended to help readers start with a reasonable number when the exact label wattage is not available.

Actual wattage can vary by model, size, age, efficiency rating, operating mode, thermostat setting, and whether the appliance cycles on and off.

Electricity rates

Many calculators use $0.18 per kWh as a default example rate. This is a rounded reference based on the average of U.S. residential electricity prices reported by the U.S. Energy Information Administration from October 2025 through March 2026. It is not a fixed national rate or a promise about any utility bill. Readers should replace it with the electricity rate from their own bill whenever possible.

For bills with multiple line items, an effective average rate can be estimated by dividing electricity-related charges by total kWh used.

Source: U.S. Energy Information Administration Electricity Data Browser, residential average price series for the U.S. total.

Recommended sources to verify your own numbers

Every appliance calculator also includes a page-specific source list and its own last-reviewed date. The sources below are the primary starting points used across the site.

Limitations

WattCostGuide estimates appliance energy cost only. Actual bills can include taxes, fixed fees, tiered pricing, demand charges, seasonal rates, delivery charges, and other appliances running at the same time.