Domera Hub · Generator sizing calculator ·
Generator sizing calculator
A preliminary estimate of emergency-generator power based on the connected essential load. It does not replace design by a qualified electrical engineer.
Enter the essential loads
Enter a total load, or break it down by system. All fields in kW.
Required real power (kW)—
Required apparent power (kVA)—
Nearest standard generator size—
Warning — preliminary estimate only. The final sizing, motor inrush currents, harmonics, voltage dips, cable length, fuel system, ventilation, location and regulatory compliance — all require calculation and design by a qualified electrical engineer. Do not order a generator based on this number alone.
How it's calculated
- Total load = Σ (emergency lighting + HVAC + lifts + pumps).
- kVA = (Σ kW × demand factor × (1 + reserve margin)) ÷ cosφ. kW is shown before dividing by cosφ.
- The standard size is the smallest value in the list (50/80/100/150/200/250/350/500 kVA) that is not smaller than the required kVA.
- A demand factor of 0.7 and cosφ of 0.8 are common rules of thumb; adjust them to the actual data.