Enter Commercial Load and Site Data
This page keeps a single-column flow, while the calculator fields use three columns on large screens, two on medium screens, and one on mobile.
Example Data Table
Use this sample to understand the relationship between diversified load, motor starting, and recommended generator size.
| Facility Type | Connected Load (kW) | Demand Factor | Largest Motor (HP) | Altitude (m) | Ambient (°C) | Recommended Size |
|---|---|---|---|---|---|---|
| Retail Plaza | 180 | 70% | 20 | 120 | 30 | 200 kVA |
| Office Tower | 320 | 75% | 40 | 450 | 34 | 400 kVA |
| Cold Storage | 540 | 78% | 75 | 700 | 36 | 700 kVA |
| Light Manufacturing | 860 | 82% | 100 | 300 | 32 | 1000 kVA |
Formula Used
These equations provide a practical planning model. Final selections should still be checked against manufacturer transient performance, voltage dip limits, and applicable electrical standards.
Assumptions used here: altitude derating is 3% per 300 m, temperature derating is 1% per 5°C above 25°C, and diesel fuel estimate is 0.24 liters per kWh.
How to Use This Calculator
- Enter the facility name and total connected electrical load.
- Apply a demand factor to reflect diversified real-world operation.
- Set the continuous portion of the load for long-duration duty.
- Enter the largest motor details and choose the start method.
- Select voltage, phase type, and the expected site power factor.
- Add future growth and reserve margin for practical expansion.
- Enter site altitude and ambient temperature for derating.
- Press the calculate button to display the sizing result above the form.
- Review the chart, summary table, current, and fuel estimates.
- Export the result summary with the CSV or PDF buttons.
Frequently Asked Questions
1) What does this calculator actually size?
It estimates a practical commercial generator rating in kVA and kW. The model considers diversified load, continuous duty, motor starting surge, reserve margin, growth, altitude, and ambient temperature.
2) Why is generator sizing expressed in kVA?
Alternators are commonly rated in apparent power because current heating depends on kVA. Real power in kW depends on the operating power factor. Both values matter during equipment selection.
3) Why is the largest motor important?
A large motor can create a short starting surge that exceeds the steady running load. That momentary kVA demand often drives the minimum generator size more than normal operating demand.
4) What is the purpose of the continuous load adjustment?
Continuous loads usually need extra headroom because they run for extended periods. This calculator applies a 125% adjustment to the continuous portion to support a conservative planning approach.
5) Why do altitude and temperature reduce available capacity?
Hot air and thin air reduce engine combustion performance and cooling effectiveness. The generator may deliver less usable output at site conditions than it would at standard reference conditions.
6) Is the fuel estimate exact?
No. It is a planning estimate based on an average diesel consumption factor. Actual fuel use changes with engine model, load profile, site conditions, maintenance state, and emission equipment.
7) Should I always choose the next higher standard size?
Usually yes for planning. Standard ratings simplify procurement and provide headroom. Final selection should still be confirmed against manufacturer motor-start curves, transient response data, and project requirements.
8) Can this replace a detailed engineering study?
No. It is an advanced screening tool. Final design should verify harmonics, step loading, non-linear equipment, starting sequence, short-circuit limits, automatic transfer strategy, and local code requirements.