Choose your backup loads
Select the appliances and systems you want available during an outage.
Free home backup power estimator
What Size Generator Do You Need?
Estimate the right generator class for your home in about 60 seconds. Choose the appliances and systems you want to keep running, and we’ll account for both running load and motor-starting surge.
✓ No signup to calculate✓ Starting watts included✓ 50 detailed sizing guides
Home Generator Sizing Calculator
Planning estimate — final sizing should be verified by a qualified installer.
This is a consumer planning estimate, not an electrical load calculation. Appliance wattage and motor starting demand vary by model, voltage, efficiency and installation. Verify equipment nameplates and local code requirements with a qualified electrician or generator installer.
A better estimate than square footage alone
Two 2,000-square-foot homes can need very different generators. Major electrical loads — especially air conditioners, heat strips and pumps — usually matter more than the house size by itself.
Account for startup surge
Motor-driven equipment can need extra power for a few seconds when it starts.
Add breathing room
The calculator adds planning headroom and rounds up to a common generator size class.
Two tools, one decision
First estimate the generator size. Then turn that size into a realistic installation budget before you talk with contractors.
Popular generator sizing guides
The site now includes 50 focused guides covering the questions homeowners search before choosing a standby generator.
Why starting watts change the answer
A refrigerator, well pump, furnace blower or central A/C may draw substantially more power for a moment when its motor starts. That is why simply adding normal running watts can understate the generator capacity you need.
Methodology note: Cummins recommends adding running loads and accounting for the highest additional starting requirement when estimating standby generator size. Final residential sizing can also involve load-management equipment, fuel-specific output, elevation and code requirements.
Local installation help
Ready for an exact generator quote?
A local installer can verify your electrical loads, fuel supply, transfer switch, placement and permitting — then quote the right system for your home.
Generator sizing FAQ
Is a 22 kW generator enough for a whole house?
It can be for many homes, but the answer depends on actual loads. Large central A/C, electric heat, water heating, EV charging, pool equipment and well pumps can change the requirement.
Should I size a generator by square footage?
Square footage is useful context, but actual running loads plus temporary motor-starting demand are more important.
Why does my A/C affect generator size so much?
Central A/C compressors are large motor loads and can require much more power for a short time at startup unless the system uses compatible soft-start or variable-speed technology.
Do I need a professional to confirm the size?
Yes for a permanently installed standby generator. A qualified installer should verify the electrical load, transfer equipment, fuel supply, placement and permitting.