What Size Generator Do You Need? - A Plain-English Sizing Guide
Last verified: September 2026
The plain-English method for sizing a portable generator — running watts, starting surge, and a formula anyone can follow, no math degree required. Rather talk it through? My number is (330) 200-8042.
Sizing a Generator, at a Glance
Sizing a generator sounds like a math problem, but it's really a list problem: decide what you want running, then add up the watts in a specific order. This guide walks through running watts, the starting surge that trips people up, reading your own appliances' nameplates, and the simple formula that ties it together. There's a printable page-by-page version up top.
Common Questions
1 What's the difference between running watts and starting watts?
Running watts are the steady power a generator can supply hour after hour. Starting (or surge) watts are the brief, much bigger jolt a motor needs for a second or two to get spinning — often several times its running watts. Size for your running total plus the single biggest surge.
2 Do I need to add up every motor's starting surge?
No — just the single largest one. Motors essentially never all start at the exact same instant, so your generator only needs to clear your steady running total plus whichever one motor's surge is biggest, with a comfortable cushion on top.
3 Where do I find the real numbers for my own appliances?
On the nameplate — a small label on the back, bottom, or inside the appliance, listing watts, or volts and amps you can multiply together. Photograph it before you shop; never guess.
4 Which of my appliances actually surge?
Anything with a motor — a fridge, freezer, well or sump pump, furnace blower, air conditioner, power tools. Lights, heaters, and most electronics draw a steady amount with no real surge.
5 How much extra headroom should I add?
A comfortable cushion above your calculated number — not right up to the edge, and not the biggest unit on the lot. Running a generator flat-out at its limit all the time runs it hot; a sensible margin keeps ordinary days easy.
6 What if my well pump is on the list?
Plan around it — a 240-volt well pump's starting surge is very likely the largest number on your whole list. It also needs a transfer switch or interlock rather than a cord; see our guide on connecting a generator.
Would You Rather I Just Help?
Sizing is arithmetic, but you don't have to do it alone. I'll help you build your must-run list, read your own nameplates, and land on a comfortable, honest number — with nothing to sell you. $99 flat for a visit, 30-day come-back-free.
Would you rather I just do this for you?
No shame in it — plenty of folks would rather hand it off, and that's what I'm here for. I'll come to your home, set it up right, and make sure it's working before I leave. Flat $99 per visit — no jargon, no upsell, and every visit is 30-day come-back-free.
Not a hardware job? I can often fix it remotely for $49 — a secure screen-share, up to 2 hours, that you watch the whole time and can end whenever (included free for $39/mo Support Plan members, and it counts toward the $99 if it turns out I need to come out).