Methodology
References and Methodology
WattCostGuide uses a simple, transparent calculation model so readers can understand and adjust every estimate on the site.
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 RateThe same conversion is used for energy consumption:
kWh = Watts / 1000 x Hours UsedWattage 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 $0.17 per kWh as a default example rate. This 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.
Recommended sources to verify your own numbers
| What to verify | Best source |
|---|---|
| Appliance wattage | Product label, nameplate, owner manual, or manufacturer specifications |
| Runtime | Your actual daily use pattern or smart plug energy monitor |
| Electricity rate | Your utility bill, utility website, or time-of-use rate schedule |
| Whole-home usage | Monthly utility bill or utility account dashboard |
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.