Whole-home generator sizing guide
Sizing a whole-home generator is less about exact math and more about clarifying what you want life to look like during an outage.
This guide gives high-level ranges and considerations so you can have a more informed conversation with installers and compare systems.
Start with your backup goals
Whole-home backup doesn't always mean every circuit must stay live during an outage. Many homeowners choose to prioritize essentials plus comfort loads rather than literally every breaker in the panel.
Think about:
- Which rooms and appliances truly matter in a multi-day outage.
- Whether you can live without electric range, dryer, or large luxury loads for short periods.
- Whether you have electric heat, well pumps, or other big draws.
Typical whole-home generator size ranges
Roughly speaking, many homes end up in these size bands:
- 10–14 kW: smaller homes or “essential circuits” coverage.
- 14–20 kW: average-size homes with central A/C and more circuits.
- 20–26 kW+: larger homes, all-electric houses, or heavier loads.
An electrician or installer can perform a more precise load calculation, but these ranges give you a starting point when comparing units.
Working with an installer
Because whole-home systems tie into fuel supply, code requirements, and utility interconnections, most people work with a licensed installer from the start. They can help:
- Estimate loads based on your panel and usage patterns.
- Select an appropriately sized standby unit.
- Plan fuel storage and automatic transfer equipment.
Tip: you can use the runtime, fuel cost, and size planners on the GeneratorCalc home page to turn these ideas into rough numbers for your specific generator and situation.