Energy Cost Calculator
See how much any appliance costs to run per day, month, and year.
Last reviewed: June 2026How the Appliance Energy Cost Calculator works
This page estimates the cost of running one appliance or device. It uses the same basic method described by the U.S. Department of Energy: daily kWh = wattage x hours used per day / 1,000. Cost is then kWh x electricity rate. The default space-heater example uses 1,500 watts for 8 hours per day, so the result is 12.00 kWh/day. At $0.12/kWh, that is $1.44 per day, $43.20 per 30-day month, and $525.60 per year.
This is a marginal-use calculator. It answers questions like "what does this heater add to my bill?" or "how much does it cost to run this dehumidifier all summer?" For a whole-house estimate, use the Electricity Bill Estimator with the total kWh from your bill.
Finding a realistic wattage
Start with the appliance nameplate, EnergyGuide label, manual, or manufacturer specification sheet. If the label gives amps instead of watts, use watts = volts x amps. In a typical U.S. 120-volt outlet, a 3-amp device draws about 360 watts. For devices with multiple settings, use the setting you actually run.
Some appliances should not be treated as if they run at rated watts all day. Refrigerators, freezers, heat pumps, window AC units, and dehumidifiers cycle. Computers, TVs, game consoles, and chargers also vary with workload and standby mode. A plug-in monitor can measure actual kWh for many 120-volt devices; hard-wired and 240-volt equipment usually needs a whole-home monitor, smart panel data, or manufacturer energy-use data.
Worked examples
Space heater: 1,500 W x 8 hours / 1,000 = 12 kWh/day. At $0.18/kWh, cost is $2.16/day, about $64.80/month. This is why resistance heat can dominate a winter bill even when the heater looks small.
LED lamp: 9 W x 5 hours / 1,000 = 0.045 kWh/day. At $0.18/kWh, that is less than one cent per day. The old 60 W incandescent equivalent would use 0.30 kWh/day under the same schedule.
Dehumidifier: A 500 W unit running 10 hours/day uses 5 kWh/day. At $0.16/kWh, that is $0.80/day or roughly $24/month. If a humid basement forces continuous operation, measured kWh is better than rated watts because duty cycle changes with humidity and temperature.
Common estimating errors
- Using square footage: this calculator does not use home size. It uses watts, hours, and rate.
- Ignoring duty cycle: cycling devices often use much less than rated watts averaged across a day.
- Using only the supply rate: the effective cost per kWh may be higher after delivery charges and taxes.
- Forgetting standby power: many electronics draw a small phantom load when off.
- Comparing appliances without use time: a high-watt microwave used 10 minutes can cost less than a low-watt device used all day.