Free sizing tool
What are you sizing a generator for?
Tap your industry, answer a few questions. We build your load list and size it against all three limits that matter.
Methodology
How a generator is actually sized
Most online calculators add up your wattage and divide by a power factor. That single number is only one of the three limits a genset has to satisfy, and it is very often not the one that decides the rating. This tool checks all three and takes the largest.
Constraint A
Steady running kVA
Every load's kW divided by its own power factor, summed, then reduced by a diversity factor because not everything runs at once, and sized so the set sits at a healthy loading target rather than flat out.
Constraint B
Motor starting step
A DOL motor draws around six times its full-load current on start. The set must absorb the biggest single start on top of everything already running, without the voltage dipping past what your equipment tolerates.
Constraint C
Engine kW ceiling
A genset rated at 0.8 power factor delivers only kVA × 0.8 in kW. Sites full of heaters, geysers and ovens run at unity power factor and hit this engine limit long before they trouble the alternator.
Why starting current matters more than connected load
A 75 HP fire pump on a direct-on-line starter draws a starting step several times larger than the entire steady load of the building it protects. Size on connected load alone and the set will stall or trip the moment that pump calls. Star-delta, soft starters and VFDs cut that inrush from roughly 6× to between 1.5× and 2.5×, which frequently drops the required rating by a whole frame size, often paying for the starter several times over.
What this tool does not account for
Site derating is excluded. Engines lose output with altitude and with ambient temperatures above 40 °C, and alternators derate in high humidity. Harmonic content from large VFD or UPS installations may call for an oversized alternator. Statutory norms (CPCB emission class, acoustic enclosure requirements, fire-pump sizing rules) apply on top. Treat the output here as a well-founded starting point, then let an RPSL engineer confirm it with a site survey.