What Size Generator Do I Need for My Home? (2026 Sizing Guide)
The most common generator mistake we see in the field is buying based on price instead of load. Undersize a unit and your central AC’s start-up surge will trip the breaker on the first hot day; oversize and you are paying for fuel you do not need. Here is the framework we use.
Step 1 — List essentials, not everything
For most homes, the essential load is: refrigerator, furnace blower, well or sump pump, a few lights, and one or two outlets for charging. That adds up to roughly 3,500-5,500 watts running.
Step 2 — Account for surge wattage
Motors (fridges, AC, pumps) draw 2-3× their running wattage on start. A typical fridge at 700W running needs 1,200W surge; a 1HP well pump at 1,200W running needs 2,400W surge. Add the single biggest surge to your total running wattage.
Step 3 — Add 20-30% headroom
Running a generator at near-max load shortens its life and burns more fuel per kWh. Headroom keeps you in the efficient zone and gives you room to add an essential later.
Step 4 — Pick a class
- Up to 3.5kW: inverter generators — RVs, electronics, partial essentials
- 5-7.5kW: open-frame portables — fridge + furnace + lights
- 10-14kW: mid-range standby — fridge + furnace + well + partial AC
- 18-22kW: whole-home standby — full home with central AC
Step 5 — Plan fuel and transfer
Calculate how many gallons per hour your size class burns at expected load, multiply by intended runtime, and add 25% buffer. Never backfeed your home’s wiring — always use a transfer switch installed by a licensed electrician.
Skip the math
Our [Generator Size Calculator](https://gas-and-diesel-engine-equipment-guide.com#eeg-generator) and [Emergency Power Planner](https://gas-and-diesel-engine-equipment-guide.com#eeg-emergency) do the math for you and recommend a matching unit on Amazon. They are free, save locally to your device, and produce printable plans.