Estimate generator size from running watts, starting watts, voltage, amps, phase type, power factor, load margin, and appliance or motor loads. This calculator helps estimate recommended generator watts, kW, kVA, surge capacity, current, load percentage, and fuel use.
Running load:
The calculator totals running watts from the entered load or detailed load rows.
Starting surge:
It adds the largest starting surge so the generator can handle motor startup without being undersized.
Recommended size:
It applies margin and continuous load factors, then estimates watts, kW, kVA, amps, and load percentage.
A generator size calculator helps estimate how large of a generator is needed for backup power, jobsite power, RV use, commercial loads, or emergency power planning.
It can help with refrigerators, pumps, HVAC equipment, well pumps, lights, outlets, tools, chargers, appliances, panels, transfer switches, and motor loads.
Your result shows recommended generator watts, recommended kW, recommended kVA, running watts, starting watts, surge watts, amps, existing generator load percentage, remaining watts, estimated runtime, and detailed load row totals.
Add the running watts of the loads you want to power, then add the largest starting surge. Add extra margin so the generator is not running at maximum capacity.
Running watts are needed during normal operation. Starting watts are extra temporary watts needed when motors, pumps, compressors, or appliances start.
Small generators are often listed in watts. Larger standby and commercial generators may be listed in kW or kVA. kVA depends on power factor.
No. This calculator gives a planning estimate. Final generator sizing and installation should account for load type, starting current, transfer switch rating, service rating, fuel supply, voltage drop, code requirements, and manufacturer instructions.