Sizing a Portable Generator to Your Real Number
Last verified: September 2026
You've added up your list — now match it to a portable. The unit's running (rated) watts should clear your steady total, and its surge watts your biggest single motor, with headroom to spare. Don't trust the big bold peak number. Rather talk it through? My number is (330) 200-8042.
Matching a Portable to Your Number, at a Glance
You've done the adding — now comes the match. A portable generator advertises two watt numbers, and each has a job. Its running (rated) watts must clear your steady total; its starting (surge or peak) watts must clear your single biggest motor's jolt — both with a comfortable margin. Don't size by the big bold number out front, which is usually the brief peak. And for a 240-volt load like a well pump, you need a 120/240-volt unit with a 240-volt outlet. This guide makes the match in plain English, with a printable page-by-page version up top.
Common Questions
1 How do I match a portable generator to my list?
Two ratings, two jobs. The generator's running (or rated) watts must clear your steady running total, and its starting (surge or peak) watts must clear your single biggest motor's jolt — with a comfortable margin on top of both.
2 Which number on the box should I trust?
The running or rated watts — the honest, steady figure. The big bold number out front is usually the brief peak, which the unit only delivers for a moment. A reputable maker lists both; compare units by the rated watts.
3 Do I need a 120/240-volt generator?
You do if you want to run a 240-volt load like a well pump or anything hardwired. Those need a 120/240-volt unit with a 240-volt outlet, connected through a transfer switch by a licensed electrician. For in-town essentials fed by cords, a 120-volt unit can be plenty.
4 Does fuel type change how much power I get?
A little. From the same engine, propane usually yields slightly less available power than gasoline. Dual-fuel units let you choose. It's a modest difference — see our guide to choosing a portable generator for the fuel details.
5 How much headroom should I leave?
Enough that the unit isn't running flat-out. Size comfortably above your calculated number, but don't massively oversize — a big engine loafing lightly all the time isn't ideal either. Our guide on margin and headroom covers the sweet spot.
6 Portable, inverter, or standby — which is right?
A portable is flexible and affordable for essentials and many rural must-run lists. An inverter unit is cleaner and quieter; a standby is permanent and automatic. See our guides on sizing an inverter generator and on a standby with load management.
Would You Rather I Just Help?
Matching a portable generator to your list is exactly the kind of thing I love helping with — no sales pitch, just honest advice. I'll help you read your nameplates, land on your running-plus-surge number, and pick a unit with the right ratings and outlets, and I'll line up a licensed electrician if you need a transfer switch. $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).