Generator Size Calculator
Work out the generator size you need from the appliances you want to run — running watts plus the largest motor's starting surge.
How to use
- 1Enter the number of each appliance you want to power at the same time.
- 2The recommended size adds the largest starting surge and a safety margin.
How it's calculated
Required = total running watts + the largest (starting − running) surge, plus a margin (20% by default). Typical appliance watts are estimates — check nameplates.
Frequently asked questions
What's the difference between running and starting watts?
Motors (fridges, pumps, AC) draw 2–3× their running power for a second or two when they start. The generator must handle that surge.
Why add a margin?
Running a generator near 100% continuously shortens its life and leaves no room for surprises.
Can a portable generator power my whole house?
Usually only essentials. Central AC and electric heating typically need a large standby generator and a transfer switch installed by an electrician.