How to calculate what an appliance costs to run
Every appliance has a running cost, and you can estimate it with two numbers: how much energy it uses, and what you pay for each unit of energy.
The two formulas
- Energy in kilowatt-hours (kWh) = watts × hours of use ÷ 1000
- Cost = kWh × your price per kWh
A watt is a rate of power. A kilowatt-hour is an amount of energy: one kilowatt used for one hour. Your bill charges for energy, so the second number is the one that matters.
Worked example
A 100 W device that runs 5 hours a day, with electricity at 17 cents per kWh:
| Step | Result |
|---|---|
| Energy per day | 100 W × 5 h ÷ 1000 = 0.5 kWh |
| Energy per month (30 days) | 0.5 × 30 = 15 kWh |
| Cost per month | 15 kWh × $0.17 = $2.55 |
| Energy per year | 0.5 × 365 = 182.5 kWh |
| Cost per year | 182.5 kWh × $0.17 = about $31 |
Appliances that cycle on and off
Many appliances do not draw full power all the time. A compressor, for example, switches on and off to hold a temperature. The formula then needs the share of time the appliance is actually running.
A hypothetical appliance that draws 600 W while running, runs 40% of the time, and is plugged in all day:
- 0.6 kW × 24 h × 0.40 = 5.76 kWh per day
- 5.76 × 30 = 172.8 kWh per month
- 172.8 kWh × $0.17 = about $29.38 per month
Where to find the watts
The label on the appliance usually lists volts and amps. Multiplying them gives watts: 120 V × 1.5 A = 180 W. That figure is normally the maximum draw, so real use is often lower. A plug-in energy meter measures the actual kWh over a day or a week and avoids the guesswork.
Common mistakes
- Mixing up kW and kWh. Power is kW, energy is kWh. Cost follows energy.
- Using the nameplate as the average. It describes the peak, not typical use.
- Forgetting standby. Some appliances use a small amount of power even when off or idle.
- Using the wrong price. Your own rate matters more than an average. See your rate versus the state average.
When the label gives annual kWh instead
Some appliances publish a yearly energy figure from a standard test. ENERGY STAR does this for certified dehumidifiers. Then you skip the hours: multiply the annual kWh by your price per kWh. Real use will differ with your home and habits, so treat it as a comparison tool. Our dehumidifier catalog does this calculation for you.
Do not convert an efficiency rating into watts. A rating such as the integrated energy factor describes output per unit of energy, not power draw.