Convert power into energy
Watts measure power at a moment; the utility bills energy over time. A 1,500-watt heater running for two hours uses 3 kWh before considering cycling or multiple settings.
Use the correct effective rate
A bill's total divided by kWh can capture supply and variable delivery charges, but fixed monthly charges should not always be attributed to one appliance.
Account for cycling and standby use
Refrigerators, air conditioners, and thermostatically controlled devices switch on and off. A plug-in energy meter or EnergyGuide estimate can be more realistic than nameplate watts times 24 hours.
Example: a 135-watt device
135 watts × 8 hours ÷ 1,000 = 1.08 kWh per day. At $0.18 per kWh, that is about $0.19 daily and $5.83 over 30.4 days if usage is consistent.
What to check before you decide
- Rate tiers, demand charges, taxes, and fixed fees are not fully modeled by one per-kWh price.
- Do not treat nameplate maximum wattage as guaranteed average consumption.
Sources behind this guide
These official and primary sources let you verify rules, definitions, and terms that may change.
FTC — How to use the EnergyGuide label↗U.S. Department of Energy — Affordable energy for consumers↗