GlenCalc

Generator size calculator

List the appliances you want to run at once with their running and starting watts (on the label or manual). Motors, like fridges and pumps, need a surge to start.

Your answer

Generator size4,740 WStarting (peak) watts
Running watts2,450 W
Largest extra starting surge1,500 W

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How we worked it out

Updated as you change the numbers.

  1. Total running watts + the largest single extra starting surge (motors start one at a time), plus the margin.

Method and assumptions

Generators are rated for running watts and a higher starting (surge) rating. Only one motor usually starts at a time, so the peak is the running total plus the biggest single surge. A transfer switch installed by an electrician is required to connect to house wiring.

Questions

What size generator runs a fridge, sump pump, lights and furnace fan?

About 4,740 W peak with a 20% margin (2,450 W running plus the fridge’s 1,500 W start surge).

Sources

Method and figures checked on . Every worked answer on this page is covered by an automated test. Found a mistake? Tell us.

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