Measure appliance electricity use and calculate annual cost
The rating plate is not your electricity bill.
A useful electricity-cost estimate starts with actual energy use and the rate you pay per kilowatt-hour. The wattage on a rating plate is not automatically an appliance’s average draw in everyday use. Virginia Cooperative Extension explains that actual consumption depends on settings and that refrigerators cycle on and off. [1]
Watts describe power; kilowatt-hours describe energy
Watts tell you how much power something draws at a given moment. Kilowatt-hours record energy used over time. At constant power, multiply watts by hours and divide by one thousand. Being plugged in does not mean an appliance draws the same wattage all day. Your estimate needs either representative average power or separate operating states.
Record a complete pattern of use
- Check that the plug-in meter, outlet and appliance are compatible and within the meter’s rating. Follow its instructions; do not open wiring or attempt to connect it to a hardwired appliance.
- Reset the energy counter and record the start time and operating conditions.
- Use the appliance normally and include the phases you want the estimate to represent.
- Record both accumulated kWh and elapsed hours. A momentary watt reading is not the same as measured energy over time.
A complete use cycle tells you more about an occasional appliance than a brief look at its peak draw. Equipment that cycles on and off needs an observation period that captures those cycles. Write down whether your reading covers active use only or includes idle time, so you can reproduce the comparison later.
Turn the reading into calculator inputs
To find average power, multiply measured kWh by one thousand and divide by the hours measured. If the reading represents a complete daily pattern including idle periods, enter that average with 24 hours of operation and zero additional standby watts. Adding standby again would count the same energy twice. Annualizing a measurement assumes the observed pattern continues.
| What you have | What to enter | Limitation |
|---|---|---|
| Measured operating power | Watts and actual operating hours | Account for standby separately |
| Energy over a complete daily pattern | Average watts, 24 hours, zero standby | The period must be representative |
| Rating plate | A starting point for an estimate | Maximum power is not average use |
| Electricity bill | Usage rate in cents per kWh | Do not add the same fixed fee to every appliance |
Worked example: same watts, different hours
These inputs are invented: 50 watts while operating, no consumption during the remaining hours and 20 cents per kWh. They are not a typical refrigerator or a surveyed electricity rate. The comparison isolates operating time. Our calculator uses 365.25 days as its average year length.
| Hours per day | Annual energy | Annual cost |
|---|---|---|
| 2 | 36.5 kWh | $7.31 |
| 4 | 73.1 kWh | $15 |
| 24 | 438.3 kWh | $88 |
Per year
73.1 kWh
Of that, running
$15
Of that, standby
$0
| Power draw when running | 50.00 |
|---|---|
| Hours a day | 4.00 |
| Kilowatt-hours a year, running | 73.10 |
| Kilowatt-hours a year | 73.10 |
| That is what it costs per year | $15 |
Assumptions behind this calculation
- Days per year: 365
- The remaining hours of the day count as standby. If you actually unplug it, enter 0 watts there.
- The wattage comes from you. The rating plate states rated or maximum power, not automatically average power. For varying consumption, use measured kWh over a representative period. If that average already includes idle periods, use 24 hours and no additional standby.
The full calculator with an example, the method and sources: Electricity Cost Calculator: Appliance Running Cost
Use your bill, then check the result
Enter your applicable usage rate from your bill. A fixed customer charge that stays unchanged is not an appliance cost you can avoid by switching that appliance off. Time-of-use pricing needs extra care: a single rate here is a simplifying assumption, so choose one that represents when the appliance actually runs.
At four operating hours per day, the example uses 73.1 kWh and costs $15 a year. This is a projection from the stated inputs, not a measurement of a particular appliance.
Repeat the measurement after a change under similar conditions. If you are considering replacement, include the purchase price and expected remaining life of the current appliance. A smaller electricity bill does not by itself make buying a replacement cheaper overall. See what unplugging actually saves for standby context, and use the switch calculator to compare tariff costs separately.
Do not present a short measurement as a guaranteed annual bill. Seasonal temperatures, settings and changes in use can alter the result. Keep a copy of the measurement period and assumptions with the estimate. That makes a later comparison meaningful instead of leaving you with two totals measured under different conditions.
What you can do about it
-
Measure
Record energy used and elapsed time together.
-
Interpret
Use your own electricity rate and a representative period.
-
Check again
Repeat the measurement after a change under comparable conditions.
Frequently asked
Can I multiply refrigerator nameplate watts by 24 hours?
That is not a reliable measurement of energy use. Power can change during operation. Use energy measured over a representative period and record its duration.
Which electricity price should I enter?
Use your applicable consumption rate in cents per kWh. A fixed charge that does not change should not be added to each appliance’s avoidable running cost.
How do I use a meter reading in kWh?
Multiply kWh by one thousand and divide by measured hours to get average watts. For a complete representative daily pattern, use that average over 24 hours with no additional standby.
Sources
- Estimating Appliance and Home Electronic Energy Use, Virginia Cooperative Extension, retrieved October 2, 2026.
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