Running Watts vs. Starting Watts — The Two Numbers, Explained
Last verified: September 2026
The one distinction that prevents most backup-power sizing mistakes: running watts keep things going, starting (surge) watts get motors going — and you size for both. Rather talk it through? My number is (330) 200-8042.
The Two Watt Numbers, at a Glance
Almost every sizing mix-up comes down to one thing: there are two watt numbers, not one. Running watts are the steady power a thing needs once it's going. Starting (surge) watts are the brief, much bigger jolt a motor needs for a second or two to get spinning. Size for your running total plus the single biggest surge, then add a margin. This guide explains both in plain English, with a printable page-by-page version up top.
Common Questions
1 What's the difference between running and starting watts?
Running (or 'rated') watts are the steady power a unit supplies 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 Which of my appliances actually surge?
Anything with a motor or compressor: fridge, freezer, well or sump pump, furnace blower, air conditioner, power tools. Lights, heaters, chargers, and most electronics draw a steady amount with no real surge.
3 Do I add up every motor's starting surge?
No — just the single largest one. Motors essentially never start at the same instant, so your unit only needs to clear your steady running total plus whichever one motor's surge is biggest, with a margin on top.
4 Where do I find these numbers for my own appliances?
On the nameplate — a small label on the back, bottom, or inside, listing watts, or volts and amps you can multiply. A motor's plate may also show a starting or 'LRA' figure. Photograph it; never guess.
5 The box shows one giant number — is that the running watts?
Usually not. The largest figure is often the brief peak. Look for the smaller 'running' or 'rated' watts nearby — that's the honest number for steady work.
6 My well pump won't start on my generator — why?
Almost always a surge that came up short. A 240-volt well pump's starting jolt is large; the unit needs enough surge headroom (and a 240-volt outlet). A soft starter can shrink that jolt — see our well-pump sizing guide.
Would You Rather I Just Help?
The two watt numbers trip up almost everyone at first — you're in good company. I'll help you tell them apart for your own appliances, read your nameplates, and land on a number you can trust, 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.
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