Generator Size Calculator
Find out roughly how many watts a generator needs to run the things you care about. Enter each appliance's running watts from its label, and the total updates.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Add up the running watts of everything you plan to run at the same time. Then add the extra surge the largest motor needs to start. Motors such as a well pump or a refrigerator compressor draw more power for a moment when they start.
Running watts are on each appliance label or in its manual. If the label gives amps and volts instead, multiply them together to get watts.
Worked example
The running watts you entered, plus a start-up surge of 1,500 watts for the largest motor, come to 4,350 watts, or 4.4 kilowatts.
Questions
Why add a surge?
Motors draw several times their running power for a moment when they start. The generator has to supply that moment as well.
Do I have to run everything at once?
No. Leave out anything you will not run together, and the total drops.
Is this the final size?
It is a planning estimate. Generator makers and electricians size a whole-house unit with their own load tables.
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