Running load
The steady-state power every load draws once it's up and going. Add it all up and that's your continuous demand. We size the set so this stays inside a safe share of its rating, with room to grow.
EGH Power Tools
Generator Sizing Calculator
Size a generator the right way: not just your running load, but the starting surge of every motor. Add your equipment and get an instant, transparent kVA recommendation, with the working shown.
- Works for any generator brand
- Real starting-load curves
- Checked by our team, 24/7
Quick start
Your loads
Add every piece of equipment the generator needs to power. Pick a type and we preset the power factor and starter for you.
Motors start top to bottom. Drag a number to change the sequence (staggered start only).
Supply & sizing assumptions
Start-sequence timing
Momentary capability is how much overload the alternator absorbs during a start at an acceptable voltage dip (a standard genset is conservative at 2×). Stagger and ramp times shape the real start sequence: longer VSD or soft-start ramps spread the load and lower the peak. Default load unit sets what new loads use; you can still change any row.
Real demand over time as each motor starts and ramps, in your chosen order. Spikes ride above the continuous rating but must stay under the momentary limit. That's the genset coping with the dip, not stalling.
Demand Continuous rating Momentary limit
Which loads drive your continuous demand, and which drive the starting peak.
Running Starting surge
Full spec breakdown
Every load, its running and starting demand, and exactly how the recommended size was reached.
Two loads decide the size
Most undersized generators get it wrong on starting, not running. Here's the model this tool uses, with nothing hidden behind a magic number.
Starting load
Motors pull a surge of current the instant they start, up to six times their running draw on direct-on-line, or almost none on a VSD. The set has to absorb that without the voltage sagging too far.
The bigger of the two
We work out both requirements separately, over a real time axis, and take the larger. Then we round up to a standard set and show you which one drove the size. No magic number, no surprises.
Why kVA, amps and kW look different
Switch the chart's unit and the kVA and amp curves match, because amps are just kVA at your voltage. The kW curve is a different shape, and that's real, not a glitch. kW is kVA multiplied by power factor, and a motor's power factor is low during the inrush, when the current is mostly reactive, then recovers as it spins up. So the kVA spike towers while the kW the engine actually feels is far smaller. That is exactly why a generator can start a motor whose starting kVA sits well above its kW rating: motor starting is limited by the alternator and voltage dip, not by the engine.
Starter types & their starting curves
The starting method sets how hard a motor hits the generator, and the shape of the curve on the profile chart. Pick the right one per load and the size drops accordingly.
| Starter type | Starting current | What it means |
|---|---|---|
| Direct on line (DOL) | ≈6× | Full locked-rotor current, held until the motor nears speed then dropping. Cheapest gear, biggest hit on the genset. |
| Star-delta | ≈2× | Starts in star at a third of DOL, with a brief bump as it transitions to delta. |
| Auto-transformer | ≈2.6× | A reduced-voltage tap holds a lower plateau, then drops. Smoother than DOL. |
| Soft starter | ≈3× | Ramps up to a current limit and holds it through an adjustable ramp time, then releases. |
| VSD / VFD | ≈1× | Practically no inrush. Current stays near rated while the drive ramps the motor up from zero over a time you set. |
This calculator gives an indicative size to guide your enquiry. Final sizing depends on your exact equipment, duty cycle, ambient conditions and load steps. Our team confirms the right set for your site, 24 hours per day, 7 days per week.
Not sure you've got it right?
Let our team size it for you
Send us your result or your equipment list. We confirm the right generator against your exact site, free, with no obligation, 24 hours per day, 7 days per week.