About Generator Sizing
About Generator Sizing
Generator Sizing is a free calculator and a set of plain guides that turn "what do I need to keep running" into a wattage number and a generator class, then show verified generators of that class.
What the site does
We answer one question: what size generator do you need? Pick a situation or list what you want running, and the calculator gives you the starting and running watts to look for, the class of generator that covers them, and models we checked against the maker's spec sheet.
We also say when a smaller, cheaper machine is enough. A lean outage list often fits a mid-size portable, and we will tell you so rather than steer you to a home standby unit.
How we size a generator
We use the same rule the generator makers publish: add the running watts of everything on at the same time, add the single largest starting surge, then add 20 percent headroom.
- Running total. The running watts of every item you want on at once.
- Largest surge. The biggest gap between one item's starting and running watts. Only one motor usually starts at a time.
- Headroom. 20 percent on top. A Cummins dealer article advises 20 to 25 percent; we use 20 and say so.
- Both numbers. A generator's peak watts must cover the starting total, and its rated watts must cover the running total, each with the headroom.
Briggs and Stratton, Champion, Generac, Cummins and Westinghouse all describe this method. Each appliance figure comes from a published wattage chart, mostly the makers' own; the calculator shows the midpoint of that source's range, and the wattage chart shows the full range across every source we read. Your appliance's label and an electrician's load calculation are always the better numbers.
Sources: Briggs and Stratton, Champion, Generac, Cummins dealer article, Westinghouse manual. Safety guidance follows the U.S. Consumer Product Safety Commission.
How we choose the generators we list
We do not test generators. Every model we list has specs taken only from the maker's own page or spec sheet, and its Amazon listing was matched by title, brand and model.
- Picks are sorted into the same size classes the calculator uses, by running watts on gasoline.
- A pick only appears in your result if it covers both of your numbers: running and starting watts.
- Every class also has an Amazon search link, so a sold-out model never leaves you at a dead end.
- We leave out unbranded listings we could not check against a spec sheet, used and renewed listings, prices, star ratings and badges.
- We never pick a home standby model. Those are permanent installs that a licensed installer sizes and quotes.
How the site makes money
The site is paid for by Amazon commissions. As an Amazon Associate, we earn from qualifying purchases.
In plain words: when you click one of our Amazon links and buy something within 24 hours, Amazon pays us a small commission. You pay the same price either way. The commission never changes which generator the calculator shows; picks follow your numbers and the maker's specs.
The site has no ads today, no paid placements, no accounts and no email sign-up.
Contact us
Email us at [email protected]. We read every message, and we fix any figure you show us is wrong.
We are not electricians, and nothing here is electrical advice. For anything that connects to your home's wiring, hire a licensed electrician. See our terms and privacy policy.