Start with the appliance label
Many appliances have a rating label on the back, underside, inside edge, or near the power cord. Look for electrical input watts (W), sometimes labeled power consumption, not a microwave's cooking output or an adapter's output rating. If the label lists a range or several modes, choose the input value 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?
Manufacturer specification example: Panasonic's NN-SN67KSAZH specifications list 1,480 W of power consumption and 1,200 W of cooking power. For a label-based electricity estimate, start with the 1,480 W input figure, not the 1,200 W output figure. These are published specifications, not this site's measurements or a constant average for every cooking setting. Check your own model.
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 | Not a direct AC watts input | Only volts and amps are available. | For AC, V x A gives VA, not necessarily real watts. Find documented input W or use measured kWh. |
| 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. | Use a labeled low-to-high range as a proxy estimate, then replace it before a decision depends on the result. |
What to do when the label lists amps instead of watts
For a DC device, volts multiplied by amps can estimate watts. For an AC appliance, that multiplication describes apparent power in volt-amperes (VA), not necessarily the real watts used; power factor, cycling, and operating mode can make the actual draw different. Prefer a labeled watt value, model documentation, annual kWh, or a clearly measured kWh period. Do not substitute an adapter's DC output or an AC VA rating for wall-side real power.
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.
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, average 30-day, and annual 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
When to stop refining a watts estimate
A mode-specific label or product-page value is usually enough for a rough household estimate. Run separate low and high settings when the appliance has distinct modes. For a cycling appliance, a high-bill comparison, or a decision that depends on a narrow result, switch to a bounded measured-kWh period instead of polishing an assumed wattage.
A similar appliance is only a labeled proxy estimate. Use a defensible low-to-high range, and do not carry that proxy into a purchase decision, a savings claim, or a bill explanation.