Generator wattage calculator
Add the running watts of everything you want to power, plus the biggest starting surge, to get the generator size you need.
How it works
Motors draw two to three times their running power for a second or two while starting. Generators can usually supply one surge at a time, so you need total running watts plus the single largest extra starting load. Adding 20% margin keeps the generator out of overload.
Quick reference
| Refrigerator | 700 | 2,200 |
| Sump pump (½ hp) | 1,050 | 2,150 |
| Window AC (10,000 BTU) | 1,200 | 3,600 |
| Space heater | 1,500 | 0 |
| Circular saw | 1,400 | 2,300 |
| Air compressor (1 hp) | 1,600 | 4,500 |
| LED lights (10) | 100 | 0 |
Typical figures for planning only. Always use the label on your appliance.
Questions
Why is carbon monoxide such a concern?
CPSC estimates that portable generators cause roughly 85 to 100 carbon monoxide deaths a year in the US. Never run one in a home, garage, basement or crawl space, even with doors open.
Inverter or conventional?
Inverter generators produce cleaner power for electronics and are quieter. Conventional ones give more watts per dollar.
Sources
Injury data for these tools
ER visits in 2025