Generator Sizing Calculator
Generator Size by Total Load
Calculate generator size from total wattage of connected loads
Itemized Load Calculation
Add up common household/building loads
Formula
Generator kVA = (Running Watts + Starting Surge) / (1000 × Power Factor) × Safety Margin | Starting Surge = Largest Motor × (Start Multiplier - 1)
Frequently Asked Questions
What size generator do I need for my house?
Most homes need 7.5-25 kW depending on the loads. A small home with basic needs (lights, fridge, sump pump) can use 7.5 kW. A medium home with central A/C typically needs 15-20 kW. A large home with electric heating and many appliances may need 25+ kW.
What is the difference between kW and kVA?
kW (kilowatts) is real power that does useful work. kVA (kilovolt-amperes) is apparent power, which includes reactive power. kW = kVA × Power Factor. Generators are often rated in kVA. With a typical 0.8 power factor, a 10 kVA generator provides 8 kW of real power.
Why do motors need extra starting power?
Electric motors draw 3-6 times their running current when starting (inrush current). This starting surge lasts 1-3 seconds. The generator must handle this surge or the motor won't start. Always account for the largest motor's starting watts when sizing a generator.
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