Generator Size Calculator
Create a preliminary portable-generator size estimate from continuous load, largest motor starting demand, reserve capacity and operating hours.
Default project preview
10,000 watts
Peak load before rounding
9,600 W
Apparent power
12.5 kVA
Output current
41.7 A
Motor-start extra
3,000 W
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Peak watts = continuous load + motor running watts × (starting multiplier − 1). Reserve is applied, then capacity is rounded up to the next 500 watts. kVA = kW ÷ power factor.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Generator Size Calculator questions
Why are starting watts higher than running watts?+
Motors and compressors can draw several times their running power during startup.
Can a generator connect directly to house wiring?+
Only through approved transfer equipment installed according to electrical code. Improper backfeeding can kill utility workers and occupants.
Does this replace an electrician load calculation?+
No. It is a preliminary planning estimate and does not account for every load characteristic or installation requirement.