Work out an appliance's electricity use and what it costs per day, month and year.
Energy use is calculated as watts × hours ÷ 1000 to get kilowatt-hours (kWh). An optional standby power adds a small continuous load for the hours the device is plugged in but idle. The daily kWh figure is then scaled to monthly (× 30.44) and yearly (× 365.25). Cost is simply kWh × the utility rate. The CO₂ equivalent uses the US EPA 2023 national average grid emission factor of 0.386 kg CO₂e per kWh.
Daily kWh
Daily kWh = (watts × hours + standby_watts × (24 − hours)) ÷ 1000
Cost
Annual cost = annual kWh × rate per kWh
Check the label on the back or bottom of the appliance, or the user manual. It may be listed as 'Rated Power' or 'Maximum Power'. If listed in amps and volts, multiply them: W = A × V.
As of 2024, the US residential average is approximately $0.16/kWh (EIA). Rates vary significantly by state — California averages ~$0.25/kWh, while Louisiana averages ~$0.10/kWh.
Many appliances draw power even when not in use — TVs with remote receivers, microwaves with clocks, phone chargers, game consoles. This 'vampire' draw is typically 0.5–5 W per device but adds up across a household.
Target the highest-wattage appliances used most often. Electric water heaters, HVAC systems and electric dryers typically dominate. Switching to LED lighting and unplugging standby devices saves a smaller but still meaningful amount.