electrical tool
Appliance Wattage Calculator
Estimate appliance watts from voltage, current, power factor, and system type.
Use appliance nameplate voltage and current when available. For three-phase AC, voltage is line-to-line voltage.
Estimated appliance wattage
1080 W
Wattage = voltage × current × power factor, with √3 for three-phase AC.
Appliance planning guide
Estimate appliance wattage from electrical values
Enter the voltage and current from an appliance nameplate when available. For AC equipment, the system type and power factor affect the estimate. A nameplate value is more useful than a generic household assumption.
Running watts and startup watts
| Value | Meaning | Where it matters |
|---|---|---|
| Running watts | Normal operating demand | Continuous generator or inverter load |
| Startup/surge watts | Temporary starting demand | Motors, compressors, pumps, and similar loads |
Formula and examples
For DC, watts = volts × amps. For single-phase AC, watts = volts × amps × power factor. For three-phase AC, watts = √3 × volts × amps × power factor.
DC example: 12 V × 5 A = 60 W.
Single-phase AC example: 120 V × 10 A × 0.8 PF = 960 W.
Practical planning
Use this page to translate measured or labeled electrical values into watts before comparing loads. Do not treat a generic estimate as a universal manufacturer specification or as proof that a generator, inverter, wiring system, or transfer setup is compatible.
Frequently asked questions
What are running watts?
Running watts are the power an appliance uses while operating normally.
What are startup or surge watts?
Startup watts are the temporary additional demand some motor-driven or compressor-based equipment can require when starting.
Should I use this estimate instead of an appliance label?
No. Use the appliance nameplate or manufacturer documentation when available. This calculator estimates wattage from voltage, current, power factor, and system type.
How does appliance wattage relate to generator sizing?
Running wattage contributes to the continuous load, while startup demand may affect the peak requirement. Generator sizing should keep those requirements separate.
Important assumptions
This is a planning estimate, not a guarantee of performance. Real equipment varies with temperature, age, power quality, duty cycle, wiring, and manufacturer specifications.