A 150 W appliance used 5 hours a day uses 274 kWh a year and costs $3.88 a month at 0.17 per kWh, or $46.54 a year.
The method
Energy in kWh = watts × hours ÷ 1,000. Here 150 W × 5 h = 0.75 kWh a day, which is 274 kWh over 365 days.
Multiply the kWh by your price per kWh: 274 × 0.17 gives $46.54 a year, or $3.88 a month.
Where to find the wattage
The nameplate or manual gives the power in watts. Heating appliances such as space heaters draw the most: a 1,500 W heater for 4 hours a day costs $31.03 a month.
Fridges and other cycling devices do not draw full power all the time, so use their yearly kWh label when you have it.
Your own price
The price per kWh is on your bill; use the all-in rate rather than the energy charge alone. The table compares common appliances at 0.17 per kWh.
| Power (W) | Hours per day | kWh per year | Cost per month |
|---|---|---|---|
| 60 | 4 | 88 | $1.24 |
| 150 | 5 | 274 | $3.88 |
| 800 | 1 | 292 | $4.14 |
| 1500 | 4 | 2,190 | $31.03 |
FAQ
Do appliances cost money when switched off?+
Many draw a small standby power. Over a year it can add up; the appliance standby calculator estimates it.
What is a kilowatt-hour?+
It is the energy used by a 1,000 W device running for one hour. It is the unit your electricity bill charges.