Commercial Generator Sizing Calculator
Accurate generator sizing for commercial and industrial applications
Commercial Generator Sizing
Determine the right generator size for your business
Recommended Generator Size:
Recommended kVA: 0.00
Recommended kW: 0.00
How to Use the Calculator
1. Enter Continuous Load
- Sum all continuous running loads (lighting, HVAC, computers, etc.) in kW.
- This is the base power your generator needs to supply constantly.
2. Identify Largest Motor Starting kVA
- Determine the starting kVA (Locked Rotor Amps / 3) of your largest motor.
- This accounts for the momentary surge required when motors start.
3. Set Power Factor & Safety Factor
- Input your system's overall power factor (typically 0.8 for commercial).
- Adjust the safety factor (e.g., 1.25 for 25% oversizing) for reliability and future expansion.
Commercial Generator Sizing Fundamentals
Continuous vs. Starting Loads
Generator sizing must account for both steady-state (continuous) loads and transient (starting) loads, especially from large motors. Starting loads can be significantly higher than running loads.
Power Factor & Safety Factor
- Power Factor (PF): Represents the efficiency of power usage. Lower PF means more apparent power (kVA) is needed for the same real power (kW).
- Safety Factor: Oversizing the generator provides a buffer for unexpected loads, future expansion, and ensures stable operation, preventing overload and premature wear.
Key Formulas:
Apparent Power (kVA) = kW / PF
Total Required kVA = (Continuous kW / PF) + Largest Motor Starting kVA
Recommended Generator kVA = Total Required kVA × Safety Factor
Recommended Generator kW = Recommended Generator kVA × PF
Calculation Formulas
1. Calculate Continuous kVA:
Continuous kVA = Continuous Load (kW) / PF
2. Calculate Total Required kVA:
Total kVA = Continuous kVA + Largest Motor Starting kVA
3. Apply Safety Factor:
Recommended kVA = Total kVA × Safety Factor
4. Convert to Recommended kW:
Recommended kW = Recommended kVA × PF
Example Calculation
Commercial Building:
Continuous Load: 80 kW
Largest Motor Starting kVA: 200 kVA
Overall Power Factor: 0.8
Safety Factor: 1.25
Continuous kVA = 80 kW / 0.8 = 100 kVA
Total Required kVA = 100 kVA + 200 kVA = 300 kVA
Recommended Generator kVA = 300 kVA × 1.25 = 375 kVA
Recommended Generator kW = 375 kVA × 0.8 = 300 kW
Result: Recommended Generator Size: 375 kVA / 300 kW