Energy Cost Calculator
Finds how much electrical energy a load uses over a period, and what it costs. Enter the power the load draws, how many hours a day it runs, for how many days, and the price of energy. Use it to estimate the running cost of an appliance, a heater, a pump or a machine, to compare two options, or to check a utility bill.
Equations
E = P·h·d C = E·r
P is the power draw in kilowatts; the page converts watts, horsepower or BTU/hr to kW for you. h is the hours of operation per day, from 0 to 24, and d the number of days. E is the energy in kilowatt-hours (kWh), the unit on an electric meter and a utility bill: a 1 kW load running for 1 hour uses 1 kWh [1]. r is the price per kWh, and C the cost in the same currency as r.
Limits and common mistakes
- Enter the average power the load actually draws, not its nameplate maximum. A refrigerator, air conditioner or heater with a thermostat cycles on and off. Either enter its running power with only the hours it runs, or measure its energy with a plug-in meter.
- A motor’s horsepower rating is its shaft output. The electrical input is larger by the motor’s efficiency, so divide by the efficiency before entering it.
- Use the total rate from your bill: the energy charge plus delivery charges, riders and taxes per kWh. Tiered, time-of-use and demand charges are not modeled; the page uses one flat rate.
- Standby power adds up. A device that draws a few watts all day uses tens of kWh a year.
Worked example
A basement dehumidifier draws 700 W and runs about 12 hours a day. Electricity costs $0.168 per kWh, all charges included. What does it add to a 31-day bill?
- Choose the Power draw unit W and enter 700.
- Enter Hours per day 12.
- Enter Number of days 31.
- Enter Rate ($/kWh) 0.168 and press Solve. The Solution shows:
Energy used: 260.4 kWh
Estimated cost: 43.7472 $
Check by hand: 0.7 kW × 12 h is 8.4 kWh a day, and 8.4 × 31 days is 260.4 kWh. At $0.168 that is $43.75 for the month, or about $1.41 a day.
