Sizing a Transfer Switch to Your Generator
Last verified: September 2026
How to make your must-run list, your generator, and the transfer switch all agree — running vs. starting watts, explained without any guessed numbers. Want help with your own gear? (330) 200-8042.
Sizing, at a Glance
Sizing means making your must-run list, your generator, and your transfer switch agree. The key idea: running watts are the steady power something uses, while starting watts are a brief, larger jolt motors need to get going. Add the running watts of everything on at once, plus the single biggest surge, leave headroom, and fit it within your generator's capacity. There's a printable 29-page version up top.
Common Questions
1 What's the difference between running and starting watts?
Running watts are the steady power a thing uses. Starting watts are a brief, larger jolt motors need to get going — often several times the running figure. Sizing has to account for both.
2 How do I find my appliances' wattage?
Check each appliance's nameplate. It may list watts directly, or volts and amps you can multiply for a rough figure (watts is roughly volts times amps). Your own labels beat any online chart.
3 Do I add up every starting surge?
No — just the single biggest one, as long as you bring circuits up one at a time so only one motor starts at once. See our load-management guide.
4 Does a bigger transfer switch give me more power?
No. The switch only routes power; it doesn't create any. Your generator's capacity is the real limit. The switch just needs to be rated to match the generator.
5 What about my 240-volt well pump?
A well pump needs a generator that provides 240-volt power and enough surge for its large starting jolt. On a well, size around the pump first — see our well-pump guide.
6 What if my list is bigger than my generator?
Trim comfort items, or stagger loads so you don't run everything at once (you rarely need to). Both let a smaller generator cover a bigger list gracefully.
Would You Rather I Just Help?
Sizing feels technical until someone sits down with you and your nameplates. That's exactly what I do — with your real numbers, no guessing, and no commission on any generator. I'll help you get it right, then hand it to a licensed electrician. $99 flat.
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).