Energy use equals watts divided by 1,000, multiplied by operating hours per day and days. A nameplate wattage multiplied by all elapsed hours can overstate consumption when a refrigerator or air conditioner cycles off. A measured consumption total over a representative period captures those off periods.
The per-kWh price can include energy and usage-based delivery charges; a separate fixed customer charge is outside this appliance calculation.
Electricity Cost: worked example
| Power draw (watts) | 1,500 |
|---|---|
| Hours used per day | 8 |
| Electricity price per kWh | $0.17 |
| Days of use | 30 |
| Cost for the period | $61 |
| Energy used (kWh) | 360 |
| Cost over a full year at this rate | $745 |
Electricity Cost: changing Electricity price per kWh
| Electricity price per kWh | Cost for the period | Energy used (kWh) | Cost over a full year at this rate |
|---|---|---|---|
| $0.14 | $50 | 360 | $613 |
| $0.15 | $54 | 360 | $657 |
| $0.17 (example) | $61 | 360 | $745 |
| $0.19 | $68 | 360 | $832 |
| $0.20 | $72 | 360 | $876 |
Electricity Cost: compare input ranges
| Input | Tested from | To | Cost for the period: low input | Cost for the period: high input | Swing |
|---|---|---|---|---|---|
| Hours used per day | 7 | 9 | $54 | $69 | $15 (25%) |
| Electricity price per kWh | $0.15 | $0.19 | $54 | $68 | $14 (24%) |
| Power draw (watts) | 1,350 | 1,650 | $55 | $67 | $12 (20%) |
| Days of use | 27 | 33 | $55 | $67 | $12 (20%) |
Electricity Cost: individual input comparisons
| Input | Value | Cost for the period | Energy used (kWh) | Cost over a full year at this rate |
|---|---|---|---|---|
| Power draw (watts) | 1,200 | $49 | 288 | $596 |
| 1,350 | $55 | 324 | $670 | |
| 1,500 | $61 | 360 | $745 | |
| 1,650 | $67 | 396 | $819 | |
| 1,800 | $73 | 432 | $894 | |
| Hours used per day | 6 | $46 | 270 | $558 |
| 7 | $54 | 315 | $652 | |
| 8 | $61 | 360 | $745 | |
| 9 | $69 | 405 | $838 | |
| 10 | $77 | 450 | $931 | |
| Electricity price per kWh | $0.14 | $50 | 360 | $613 |
| $0.15 | $54 | 360 | $657 | |
| $0.17 | $61 | 360 | $745 | |
| $0.19 | $68 | 360 | $832 | |
| $0.20 | $72 | 360 | $876 | |
| Days of use | 24 | $49 | 288 | $745 |
| 27 | $55 | 324 | $745 | |
| 30 | $61 | 360 | $745 | |
| 33 | $67 | 396 | $745 | |
| 36 | $73 | 432 | $745 |
Electricity Cost: combined input changes
| Electricity price per kWh / Power draw (watts) | 1,200 | 1,500 | 1,800 |
|---|---|---|---|
| $0.14 | $40 | $50 | $60 |
| $0.15 | $43 | $54 | $65 |
| $0.17 | $49 | $61 | $73 |
| $0.19 | $55 | $68 | $82 |
| $0.20 | $58 | $72 | $86 |
Electricity Cost: which assumptions move the result?
Electricity Cost: values and definitions
| Quantity and definition | Value used |
|---|---|
| Power draw (watts) — Printed on the appliance's label or in its manual. | 1,500 |
| Hours used per day | 8 |
| Electricity price per kWh — Found on your bill, in dollars per kilowatt-hour. | $0.17 |
| Days of use | 30 |
| Cost for the period | $61 |
| Energy used (kWh) | 360 |
| Cost over a full year at this rate | $745 |
Electricity Cost: half and double Hours used per day
| Hours used per day | Cost for the period |
|---|---|
| 4 | $31 |
| 8 | $61 |
| 16 | $122 |
Many utilities use tiered or time-of-use rates, so the marginal price differs from the average. Appliances draw less than their label wattage most of the time, and standby power adds a little. Motors and compressors have starting surges.
Demand charges apply to some commercial customers.
Electricity Cost: formula
Common error: Treating the wattage on the label as steady draw. Thermostat-controlled devices cycle, so a fridge or heater draws its full wattage only part of the time.
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Running cost is a multiplication of power, time and price, and time is the number people misjudge. A 1,500 watt heater for eight hours a day uses 360 kilowatt-hours in a month and costs $61.20 at 17 cents. The same wattage on for one hour costs pennies.
The annual figure shows what the habit costs, not what one evening costs.
At a flat assumed per-kWh price, doubling an appliance's operating hours doubles modeled energy use and cost. Changing hours does not change the entered power rating.
Estimate lighting savings on the LED savings calculator, vehicle charging on the EV charging cost calculator, and solar output on the solar panel calculator. The generator size and battery runtime pages cover backup power, and the watts to amps calculator sizes circuits.
How do I find how much an appliance costs to run?
Divide its watts by 1,000, multiply by hours used and by your price per kilowatt-hour.
Which appliances use the most electricity?
Heating and cooling equipment, water heaters and dryers use the most, while lighting and electronics use comparatively little.
Should I use the wattage on the label?
A nameplate wattage is a rated value, not a record of energy used over a month. For an appliance that cycles, multiplying that value by every elapsed hour can overstate consumption.