Generator Sizing (DC) Calculator

Size standby generators for data center backup power with altitude/temperature derating and redundancy configurations.

Inputs

IT load (kW)

PUE

Redundancy Mode

Altitude (ft above sea level)

Max ambient temp (°F)

Power factor

Max step load (%)

Tab to move between fields

Results

Generators needed

Generator size (kVA each)500

Total installed capacity (kW)1,200

Required capacity (kVA)938

Facility load (kVA)938

Derating (%)0%

Load transfer steps4

48-hr fuel (gallons)1,890

How to Use This Calculator

Enter total critical IT load in kW and UPS efficiency.
Set transfer switch transfer time and battery runtime.
Input generator loading factor and altitude derate.
Review the minimum generator kW rating and recommended kVA size.
Add N+1 redundancy capacity for critical data center applications.

How the result changes with IT load (kW)

IT load (kW)	Generators needed
10,000	6
35,000	18
65,000	32
90,000	44

What each input means

IT load (kW): Total IT equipment power draw in kilowatts.
PUE: Power Usage Effectiveness (total facility load = IT × PUE).
Redundancy Mode: Select generator redundancy configuration
Altitude (ft above sea level): Site altitude. Generators derate 3.5% per 1000ft above 1000ft.
Max ambient temp (°F): Hottest expected ambient temperature. Derating starts above 104°F.
Power factor: Generator power factor. Standby: 0.8, prime: 0.8-1.0.
Max step load (%): Maximum percentage of generator capacity that can be applied in a single step.

What each result means

Generators needed: Number of generator units required for the chosen redundancy.
Generator size (kVA each): Rating of each generator unit in kVA.
Total installed capacity (kW): Total generator capacity in kilowatts.
Required capacity (kVA): Minimum generator capacity after derating.
Facility load (kVA): Total facility load in kVA (before derating).
Derating (%): Combined altitude and temperature derating percentage.
Load transfer steps: Number of sequential load steps to bring IT load online.
48-hr fuel (gallons): Diesel fuel needed for 48 hours of runtime at 75% load.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
IT load (kW) = 500, PUE = 1.5, Redundancy Mode = 1, Altitude (ft above sea level) = 500 = 7 input(s) provided
Calculate Generators needed
3 = 3
Calculate Generator size
500 = 500
Calculate Total installed capacity
Total installed capacity = totalInstalledKva * powerFactor
1200 = 1200

Engine last updated August 5, 2026.

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