Select the appliances that must run together, account for motor startup demand, and calculate practical continuous and peak wattage targets.
Select loads that may run together
These presets are planning estimates. Replace them with nameplate or manual values before buying.
Kitchen presets show electrical input, not heat output. Choose either the full electric range or its individual oven and burner loads to avoid counting the same appliance twice. Many built-in ranges need 240V and a properly rated transfer connection.
Add one custom load
How to calculate generator size
Add the running watts of everything that may operate at the same time. Then add the largest extra startup surge from a refrigerator, freezer, pump, furnace blower, or air conditioner. The calculator applies 25% continuous headroom and a smaller peak margin so the generator is not planned at its limit.
Kitchen appliances can change the answer quickly
Microwaves and countertop ovens commonly draw far more power than their cooking-output labels suggest. An electric stovetop burner or built-in oven may require 240V; a full electric range can dominate the entire load calculation. Select only the kitchen loads you expect to run at the same time, and do not count a full range again as separate burners and oven. Confirm actual input ratings and the approved connection plan before purchasing a generator.
Typical generator-size classes
2,000–2,500W inverter generator: refrigeration, lights, internet, charging, and a few small devices.
4,500–5,000W class: a broader essential-load plan that may include one pump, furnace blower, or window air conditioner.
7,500–9,500W class: selected household circuits and larger startup loads, usually with a professionally planned transfer connection.
10,000W and above: high-demand systems where fuel use, 240V requirements, placement, and electrician review become especially important.
Safety: Operate portable fuel-burning generators outdoors, at least 20 feet from the home, with exhaust directed away from doors, windows, and vents. Never backfeed a home. Use a qualified electrician for an inlet, transfer switch, or approved interlock.
Wattage is not the only requirement
Verify voltage, receptacles, breaker rating, fuel-specific output, noise, runtime, weight, and carbon-monoxide shutoff features. A generator with enough advertised watts still cannot supply a 240V well pump if it provides only 120V.
Measure before buying
Preset values are planning examples. Read appliance labels and manuals, and use measured values where possible. Pumps and older compressors can have substantially different surge behavior from generic estimates.
Many will, provided the unit can handle the refrigerator’s startup surge and the other simultaneous loads remain modest. Verify the refrigerator and generator specifications.
Do I add every appliance’s starting watts together?
Usually not. A practical estimate adds all simultaneous running loads plus the largest likely additional motor surge, unless your operating plan allows multiple large motors to start together.
Should I size using gasoline or propane output?
Use the rating for the fuel you expect to run. Dual-fuel generators commonly produce less output on propane.
What Size Generator Do I Need? Free Calculator | Essential Reserve