Standby generator sizing
Budget steady-state generator capacity using simultaneous demand, reserve and the manufacturer site-capacity factor.
Enable JavaScript for live calculations. Read the method and default example below.
Method and assumptions
- Capacity = simultaneous load × (1 + reserve / 100) / (power factor × site-capacity factor).
- Voltage is across the load for single phase and line-to-line for three phase.
Before using the result
- Steady-state budget only. Motor starts, load steps, nonlinear loads, permissible voltage/frequency dip and set duty must be checked with the generator manufacturer. No set or ATS model is selected.
Worked example
Illustrative default inputs. Enter your project values above.
- Connected load
- 250 kW
- Supply arrangement
- Three phase — balanced
- Supply voltage
- 415 V
- Load power factor
- 0.8
- Simultaneous load
- 80 %
- Largest motor within connected load
- 30 kW
- Planning reserve
- 20 %
- Manufacturer site-capacity factor
- 1
Default results
- Steady-load capacity budget
- 300 kVA
- Active-power capacity budget
- 240 kW
- Current at entered voltage
- 417.4 A
Choose a reference or send your BOQ
Compare relevant product families, then confirm the exact rating, control supply and duty. Price and availability are confirmed with your enquiry.
Technical references
These references support planning. The exact model documentation and a project-specific engineering review govern the final specification.