To calculate generator power, first sum the kilowatts (kW) of all connected devices, then multiply by 1000 to get watts. Divide by the power factor (typically 0.8) to get apparent power in kilovolt-amperes (kVA). For a three-phase system, you must also multiply by the square root of 3 (approximately 1.732). Add a safety margin (usually 10-20%) to the total to avoid overloading, and consider factors like high-altitude or high-temperature operation. 
Steps to Calculate Generator Power

1. 1. List All Devices:
   Create a list of all appliances, lights, and equipment that will be powered by the generator. 
2. 2. Find Each Device's Wattage:
   Determine the wattage for each device. This is often listed on the device's label or in the owner's manual. 
3. 3. Sum Total Wattage:
   Add up the wattage of all the devices that will be running simultaneously. 
4. 4. Convert to kW (if necessary):
   If the total wattage is a very large number, divide it by 1000 to get the power in kilowatts. 
5. 5. Consider the Power Factor:
   Apply a power factor (PF) of 0.8, which is a common value, to account for the difference between real power (kW) and apparent power (kVA). 
   • For single-phase power: kVA = kW / 0.8 
   • For three-phase power: kVA = kW / (1.732 x 0.8) 
6. 6. Add a Safety Margin:
   Add a safety margin (e.g., 10% or 20%) to the calculated kVA value to ensure the generator isn't constantly running at its maximum capacity, which can reduce its lifespan. 
7. 7. Adjust for Operating Conditions:
   If the generator will operate at high altitudes or extreme temperatures, it may need to be oversized to compensate for the reduced efficiency. 

Formulas for Generator Calculations
The basic formulas you'll need are: 

• Single-Phase:
  • kVA = (Amps x Volts) / 1000
  • kW = (Amps x Volts x Power Factor) / 1000
• Three-Phase:
  • kVA = (Amps x Volts x 1.732) / 1000
  • kW = (Amps x Volts x 1.732 x Power Factor) / 1000