Home Generator Sizing Calculator
Sizing a backup generator wrong means either wasting money on excess capacity or not having enough power when you need it. This calculator adds up running watts for common household loads and factors in the extra surge watts needed when motors like refrigerators and well pumps start up.
About this calculator
Calculate the generator wattage size you need based on your household's essential and optional appliances, including startup surge power.
Frequently Asked Questions
Why does surge wattage matter?
Motors in appliances like refrigerators, well pumps, and AC units need a short burst of extra power (2-3x running watts) to start up. Your generator must handle the single largest surge on top of everything else already running.
Should I size up beyond the calculated number?
Yes, most experts recommend a 10-20% safety margin to avoid running your generator at maximum capacity constantly, which shortens its lifespan.
Can I run everything at once on a smaller generator?
You can stagger appliance use — for example, avoid running the microwave and well pump simultaneously — to get by with a smaller generator, but it requires manual load management.