Generator Size Calculator — Whole-House Backup Sizing
Quick answer: Add appliances with their wattage, see the recommended generator size with safety margin.
Calculate exactly what size generator you need for your home, RV, or jobsite. Add each appliance with its running and starting watts — the calculator finds the largest single surge plus total running load to recommend a properly-sized generator.
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Last reviewed: April 2026Report an error
Appliances
Quick add:
Recommended Generator Size
4,500 W
Total running watts: 1,850 W. Peak surge: 3,350 W. Recommended: 4,500 W (mid portable, includes 25% safety margin).
Running Watts
1,850 W
Peak Surge
3,350 W
Category
mid portable
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How to Use This Generator Size Calculator
- 1Add each appliance: name, count, running watts, starting (surge) watts.
- 2Find watt ratings on the appliance's nameplate or its manual.
- 3Read total running watts and peak starting watts.
- 4Buy a generator at or above the recommended size.
Frequently Asked Questions
- Running watts is the steady-state load. Starting (surge) watts is the brief spike when motors fire up — refrigerators, AC compressors, well pumps need 2-3x running watts for the first second.
- A 7,500-watt portable can run essentials. Heavy loads (central AC, electric range, water heater, dryer) usually require 10,000+ watts and a transfer switch.
- Inverter generators produce cleaner power (safer for laptops, TVs) and are quieter and more efficient at partial load. Conventional are cheaper per watt and better for tools.
- Yes if you want to power circuits hardwired into your panel. A transfer switch costs $300-$1500 + electrician install but is far safer than running extension cords.
- A 5kW generator at half load burns ~0.5 gallons/hour of gasoline. Propane is ~50% more volume. Diesel is most efficient but louder and pricier.
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