🔋Generator Size Calculator
Pick what you want to keep running during an outage and get a generator size in watts.
What you want to power
Recommended generator
5,000 watts
2,850 W running + 1,500 W largest start-up surge
running watts
2,850
largest surge
1,500
peak watts
4,350
recommended
5,000 W
Connecting a generator to your home's wiring requires a transfer switch installed by a licensed electrician — never backfeed through an outlet.
Rather hire it out?
Compare prices from pros near you — it's free.
How it works
- Running watts = sum of every selected appliance.
- Starting surge = the biggest extra kick any one motor needs to start (starting watts − running watts). Only one motor usually starts at a time.
- Recommended size = running + largest surge + 10% headroom, rounded up to a common generator size.
Worked example
Fridge (700/2,200 W), sump pump (1,050/2,150 W), furnace fan (800/2,350 W), lights (300 W) and TV (300 W):
- Running = 3,150 W
- Largest surge = 2,350 − 800 = 1,550 W
- 4,700 × 1.1 = 5,170 → 7,500 W generator
Safety
A home connection requires a transfer switch installed by a licensed electrician. Never plug a generator into a wall outlet.
Questions people ask
Motors need a short burst of extra power to start. Running watts is what they need once going.
More calculators you might like
Electricity Cost
How much does that space heater really cost? Pick an appliance, hours a day and your rate.
Solar Panel
From your monthly use (or bill), find the solar system size, panel count and roof space you'd need.
Wire Size
Enter the load and distance to see the smallest wire that handles both the amps and the voltage drop.
Email me my results
Pop in your email and keep your numbers handy at the store.
Last updated October 8, 2026. These results are friendly estimates to help you plan — always double-check before buying or making big decisions.