Generator Size Calculator
Calculate the right generator size in kW for your home or job site. Enter total wattage and motor starting requirements to get a recommended generator size.
W
Recommended Generator Size
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Peak (Starting) Watts —
Recommended Wattage (w/ buffer) —
Extended More scenarios, charts & detailed breakdown ▾
W
Recommended Size
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Peak Watts —
Generator Category —
Professional Full parameters & maximum detail ▾
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W
gal
Sizing
Recommended kW —
Required kVA —
Operation
Est. Fuel Consumption —
Est. Run Time per Tank —
Installation
Transfer Switch —
Voltage Note —
How to Use This Calculator
- Enter your total running watts (sum of all appliances you want to run simultaneously).
- Select a starting watts multiplier — use 1.5x if you have motors (fridge, AC, sump pump).
- Results show recommended generator size in kW with a 20% safety buffer.
Formula
Peak watts = running watts × starting multiplier
Recommended kW = peak watts × 1.2 (20% buffer) ÷ 1000
Example
Example: 5,000 running watts × 1.5 starting multiplier = 7,500 peak watts × 1.2 buffer = 9 kW generator recommended.
Frequently Asked Questions
- Add up the running watts of all appliances you want to power. Then account for starting watts (motors need 1.5–3x running watts to start). Add a 20% buffer and that is your minimum generator size.
- Running watts is the continuous power an appliance needs. Starting watts (also called surge watts) is the extra power needed for 1–2 seconds when a motor starts up — typically 1.5–3x the running watts.
- A typical 2,000–3,000 sq ft home needs a 22–30 kW standby generator to power everything. For essentials only (lights, fridge, sump pump, a few outlets), a 7–10 kW generator is usually enough.
- Inverter generators are quieter, more fuel-efficient, and produce cleaner power safe for electronics. Conventional generators are louder but cheaper for the same wattage — better for construction sites and heavy tools.