How to Calculate What Size Generator You Need (Running + Starting Watts)
The list, with sourced watts
| Appliance | Running watts | Starting (surge) |
|---|---|---|
| Refrigerator/freezer (standard household) | 1,000 | 2,200 |
| Sump pump (1/3 HP) | 800 | 2,100 |
| Window AC (10,000 BTU) | 1,200 | 2,000 |
The arithmetic
+ largest single starting surge: 1,300W
= peak demand: 4,300W
× 1.2 headroom → recommended rating: ~5,200W
Generators that cover this (from our verified catalog)
Spec: manufacturer
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See Westinghouse WGen5300 on Amazon →Spec: authorized_dealer
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See Generac GP6500 COsense (76803) on Amazon →Adjust this list in the calculator →
How many watts do I need for running + starting watts?
3,000 running watts, 4,300W at startup, ~5,200W rated recommended with headroom.
Why do starting watts matter?
Motor-driven appliances (fridges, pumps, AC compressors) briefly draw 2–4× their running watts at startup. A generator must cover running load plus the largest single surge, or the motor stalls and breakers trip.
Is a bigger generator always better?
No — oversized open-frame units burn more fuel and run louder. Size to your real list with ~20% headroom.
Sources
- Wattage Worksheet '3R0WATTGUIDE' (generator reference guide, Home Depot-hosted PDF) (vendor)
- A-iPower Wattage Chart (Sam's Club-hosted PDF) (vendor)
- Champion Power Equipment 'Choosing a Generator' wattage flyer (manufacturer)
- Howell-Oregon Electric Cooperative generator sizing chart (utility)
Figures are conservative sizing values chosen from the range these sources report. Your appliance's nameplate is authoritative.