Generator Sizing, Starting Surge Watts & Amps Calculator
Size emergency backup and jobsite generators. Calculate continuous running watts, inductive motor starting surge watts (Locked Rotor Amps), 120V/240V breaker amps, and fuel runtime requirements with a 20% safety margin.
Essential Appliances & Motors to Power
800 W / 2,200 W
1,050 W / 3,100 W
800 W / 2,000 W
750 W / 1,800 W
1,000 W / 1,000 W
350 W / 350 W
3,500 W / 9,500 W
Custom Additional Loads
Recommended Generator Capacity
Standard Portable (7.5 kW)
7,500W Running / 9,500W Surge
Includes recommended 20% continuous capacity safety buffer
Total Continuous Running Watts
4,750 Watts
5,700W buffered (with 20% margin)
Peak Starting Surge Watts
6,800 Watts
Largest single motor surge: 3,100 W (Well Pump)
Electrical Connection & Amperage Specs
240V Split-Phase Current:
31.3 Amps (Requires 30A or 50A Inlet)
120V Total Current Draw:
39.6 Amps continuous
Estimated Fuel Burn Rate:
~0.65 gal/hr gasoline (@ 50% load)
Frequently Asked Questions
Why add a 20% safety margin when sizing a generator?
Running a generator continuously at 100% capacity causes severe engine strain, voltage drops (brownouts that damage electronics), and rapid engine overheating. Generators operate most efficiently and reliably at 50%–75% of rated load.
What is the difference between a bonded neutral and floating neutral generator?
When connecting a generator to a home electrical breaker panel via a transfer switch, the National Electrical Code (NEC) typically requires a floating neutral to prevent dangerous dual ground loops.