Start with the appliance label
Many appliances have a rating label on the back, underside, inside edge, or near the power cord. Look for watts, shown as W. If the label lists a range or several modes, choose the number that best matches how you normally use the appliance.
Check the manual or product page
If the label is hard to read, search the model number on the manufacturer's website or product manual. Product pages may list rated power, maximum power, typical power, or standby power. Rated power is a practical starting point.
Which wattage source should you use first?
Different wattage sources are useful for different jobs. Start with the clearest source for the mode you use. Measurement is optional and most useful when the device cycles or changes power draw.
Scroll horizontally to see all columns.
| Wattage source | Confidence for a rough estimate | Use it when | Boundary |
|---|---|---|---|
| Mode-specific watts on a label or manual | Strong | The listed setting matches the way you normally run the appliance. | Enter that watt value with a runtime that matches the same use case. |
| Rated or maximum watts from a manual or product page | Useful fallback | No clearer mode-specific value is available. | Treat it as a planning estimate, especially for devices with modes or cycles. |
| Amps x volts | Fallback conversion | The device lists amps but not watts. | Confirm the voltage and mode if possible before treating it as normal draw. |
| Measured kWh | Alternate path for variable loads | The appliance cycles, changes modes, or runs for long periods. | Use the measured kWh with a kWh-to-cost path instead of forcing watts. |
| Similar appliance estimate | Weak fallback | No label, manual, product page, or measured value is available. | Replace it later with a model-specific or measured input if the estimate matters. |
What to do when the label lists amps instead of watts
If a device lists amps, you need voltage too. A simple estimate is watts = amps x volts. For example, 2 amps at 120 volts is about 240 watts; use your local voltage if it is different. This is still an estimate, especially for devices with motors or variable power draw.
Rated wattage vs real-world wattage
Rated wattage is useful for planning, but real use can be lower or change by mode. A heater may run near its rated wattage, while a refrigerator, dehumidifier, or air conditioner may cycle on and off. A plug-in power meter can give a more realistic reading when accuracy matters.
Examples
- A portable heater often lists a clear wattage such as 750 W or 1,500 W.
- A fan may list lower wattage, but long overnight runtime can still add up.
- A desktop PC can vary by workload, monitor count, and power settings.
- An air purifier may use different wattage in sleep, medium, and high modes.
- A dehumidifier may cycle, so average runtime matters as much as label wattage.
Use wattage with the site calculators
After you find the wattage, use the Watts to kWh Calculator if you want to convert power and runtime into energy use.
If you also know your electricity rate, use the Appliance Electricity Cost Calculator to estimate daily, monthly, and yearly cost. If you only want to compare one hour of use, use the Electricity Cost Per Hour Calculator. If you are not sure which page to use first, the Electricity Cost Calculators hub explains the options. To see the calculation steps after you have a wattage number, read how to calculate electricity cost from watts.
Common mistakes when entering wattage
- Entering volts or amps in a field that expects watts
- Using standby wattage when estimating active running cost
- Using maximum wattage for a device that normally runs in a lower mode
- Forgetting to multiply by quantity when several devices run together
FAQ
How accurate does the wattage need to be?
For a practical household estimate, a reasonable label or product-page value is usually enough. For a variable appliance or a high-bill comparison, measured wattage or measured kWh may be better.
What if an appliance has multiple wattage settings?
Use the setting you normally use, or run separate estimates for low and high settings to see the range.
Can I use estimated wattage from a similar appliance?
Yes for a rough estimate, but model-specific labels or manuals are better when you need a more reliable result.