What size generator do I need for my house?

A 7,000-10,000 watt generator covers most critical home loads (refrigerator, lights, HVAC, well pump). A whole-home standby generator is typically 14,000-20,000 watts.

What is the difference between running watts and starting watts?

Running watts (continuous watts) is the power needed to keep a device running. Starting watts (surge watts) is the extra power needed when a motor starts — typically 2-3× running watts.

Can I run an air conditioner on a generator?

Yes, but HVAC has very high starting watts (3× running). A 3-ton central AC unit (3500W running) may need 10,500W to start, requiring at least a 12,000W generator.

Is a standby generator or portable generator better?

Standby generators start automatically, run on natural gas/propane, and power the whole home. Portable generators are cheaper but require manual setup and run on gasoline.

How long can a generator run continuously?

Most portable generators can run 8-12 hours on a tank of gas. Standby generators on natural gas or propane can run indefinitely as long as fuel is available.

Generator Size Calculator — Running & Starting Watts

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Quick Answer

To size a generator, total your running watts for all critical loads, then add the highest single motor starting surge (2-3× running watts for HVAC or pumps), and select the next generator size above 125% of total running watts. A 7,500-10,000 watt generator covers most home essentials.

Use the Generator Size Calculator below to get instant results.

Generator Size Calculator

Select critical loads to size a backup generator. Running watts determine continuous capacity; starting watts account for motor surge.

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Cite This Tool

Generator Size Calculator. (2026). Electrical Calculators Online. Retrieved from https://electricalcalcpro.com/generator-size-calculator/

Generator Size Calculator

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