What size generator do I need?
Check off everything you want to run at the same time. We'll add up the running watts, account for motor starting surges, add sensible headroom — and tell you the generator size to buy. Free, no signup.
1. Select your appliances
Wattages are preloaded from manufacturer sizing guides and typical nameplates. Adjust any value to match your appliance's nameplate — yours is the number that counts. sizing-guide = published guide value · estimate = typical/inferred value.
Learn how generator sizing works
Running vs. starting watts, explained
Why a 250 W fridge can trip a 2,000 W generator — and the simple formula pros use.
Inverter vs. conventional generators
Clean power, noise, fuel use, and cost per watt — which type fits your use case.
What size for home backup, camping, or jobsite?
Typical wattage ranges and example load lists for the three most common uses.
What will popular generator sizes run?
What will a 3500 watt generator run?
A 3,500 W portable (about 2,800 running watts) covers the outage basics: refrigerator and freezer, lights, phone and laptop charging, WiFi, a sump pump, and a microwave used on its own. It's the sweet spot for apartments and small homes without a well pump.
What will a 7500 watt generator run?
A 7,500 W portable (about 6,000 running watts) is the homeowner's sweet spot: refrigerator, freezer, well pump up to 3/4 HP, gas furnace blower, lights, TV, and a window AC or microwave. It won't run central air, an electric dryer, or an electric water heater alongside everything else.
What will a 12000 watt generator run?
A 12,000 W portable (about 9,600 running watts) approaches whole-home coverage for essentials and can start a small central AC with a soft-start kit. Beyond this, permanently installed standby generators (20 kW+) take over.
Generators worth a look, by size
When you're ready to buy, these are the categories to compare. We don't sell generators — compare specs and reviews before buying.
~3,500 W inverter — camping & RV
Quiet, fuel-efficient, safe for electronics. Enough for an RV AC or microwave plus basics.
Compare 3500W inverters →~7,500 W dual-fuel — home backup
The homeowner sweet spot: well pump, furnace blower, fridge, freezer, and lights together.
Compare 7500W dual-fuel →~12,000 W portable — near whole-home
Maximum portable power before stepping up to an installed standby unit.
Compare 12000W portables →Affiliate disclosure (template): When this site monetizes, links marked as affiliate links may earn us a commission at no extra cost to you. That never affects our sizing math or recommendations.
Generator sizing FAQ
What size generator do I need to run my house?
For essential circuits — refrigerator, freezer, well or sump pump, furnace blower, and lights — most homes need 5,000 to 7,500 running watts. Use the calculator above with your actual appliances for a precise number.
What is the difference between running watts and starting watts?
Running watts is continuous draw; starting (surge) watts is the brief 2–3x burst motors need to start. A 250 W fridge may need 1,200 W for a few seconds when its compressor kicks on. Full explanation →
What will a 7500 watt generator run?
About 6,000 running watts: fridge, freezer, well pump to 3/4 HP, furnace blower, lights, TV, WiFi, plus a window AC or microwave. Not central AC, electric dryers, or electric water heaters with other loads.
Should I get an inverter or conventional generator?
Inverter for camping, RVs, and electronics (quieter, cleaner power, better fuel economy at partial load). Conventional open-frame for maximum watts per dollar on jobsites and basic backup. Full comparison →
Can I run a portable generator in my garage?
No — carbon monoxide kills. Outdoors only, 20+ feet from doors, windows, and vents, with a CO alarm inside. Never backfeed a panel; use a transfer switch or interlock installed by an electrician.
How do I connect a portable generator to my house?
Via a manual transfer switch or breaker interlock kit and an outdoor inlet box, installed by a licensed electrician. Extension cords work for individual appliances. Never plug a generator into a wall outlet.