Generator Sizing Calculator

Total running and starting (surge) watts needed for backup power. Add appliances, get the right generator size with margin built in.

Check the boxes for appliances you want to run simultaneously. Surge watts (for motor startup) are included automatically.

Generator sizing tips

Running watts are what an appliance needs to keep operating. Surge watts are the brief spike when motors start.
Generators are rated for both - buy one whose surge rating covers your worst-case (e.g., AC compressor + fridge starting together).
Add 20% safety margin for unexpected loads. Don't run a generator at 100% capacity continuously.
Whole-home backup: 5,000-7,500 watts for essentials. 10,000+ watts for central AC and electric ranges.
Inverter generators produce cleaner power (safer for electronics) but cost 30-50% more than open-frame.