How to Size a Data Center Generator: Step-by-Step Guide
Size a data center generator to total IT load, PUE, redundancy and tropical derating — with a worked example and an instant calculator.
Take the total IT load, multiply by PUE to cover cooling and mechanical systems, add house loads, then apply a redundancy factor (N+1 or 2N) and derate for the local climate. The result is the installed generator capacity you need.
The 6-step sizing method
Each step below feeds the next. Work in kW, then convert to kVA (kVA = kW ÷ power factor, typically 0.8).
Total IT load
Sum current and planned rack power (kW). This is the critical load the data center must never lose.
Apply PUE
Multiply IT load by PUE to include cooling, CRAC/CRAH and mechanical. A PUE of 1.4 means 1 MW IT needs 1.4 MW supported.
Add house loads
Lighting, BMS, security, controls — typically a few percent on top.
Redundancy factor
Add spare capacity per Uptime Tier: N+1 (one spare unit) for Tier III, 2N (full duplication) for Tier IV.
Tropical derate
High ambient temperature and humidity reduce engine/alternator output — oversize and up-rate cooling for Singapore/SEA.
Step / block load check
The genset must absorb the full block load in one step when the UPS transfers (per ISO 8528-G3).
Worked example: a 2 MW Tier III data hall in Singapore
- IT load = 2,000 kW
- × PUE 1.4 → facility load = 2,800 kW
- + house loads (~5%) → 2,940 kW
- ÷ tropical derate 0.90 → effective sizing = ~3,267 kW
- scs-series usable ≈ 1,920 kW/unit → ⌈3,267 / 1,920⌉ = 2 units (N)
- Tier III → N+1 → 3 units total
Result: 3 × scs-series 3,000 kVA in N+1 (≈ 9,000 kVA installed).
Indicative — final design validated by ASO engineers.
Try it: sizing calculator
Estimate units & redundancy for an ASO scs-series solution (3,000 kVA / ~2,400 kW per unit).
See the full technical overview, Tier table and sizing tool.
Read the Data Center Generators hub →Data center generator sizing FAQs
How do you size a data center generator?
Total IT load × PUE + house loads, then apply a redundancy factor (N+1 or 2N) and derate for climate. See the 6-step method and worked example above.
What is PUE and why does it matter for sizing?
PUE (Power Usage Effectiveness) is total facility power ÷ IT power. It captures cooling and mechanical overhead, so a PUE of 1.4 means you support 40% more than the raw IT load.
How much should I oversize for redundancy?
Tier III uses N+1 (one spare unit); Tier IV uses 2N (full duplication). N+1 adds one unit; 2N roughly doubles the plant.
Does Singapore's tropical climate change the sizing?
Yes — sustained heat and humidity derate output (around 10%), so you oversize and up-rate cooling versus a temperate-climate site.
What is step load or block load acceptance?
When the UPS transfers, the generator must take the full load in one step. ISO 8528-G3 and a PMG alternator help meet this.
kW or kVA — which do I size in?
Work the load in kW, then convert to kVA using the power factor (kVA = kW ÷ 0.8). Generators are rated in kVA.
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For operators, EPC contractors and distributors across Singapore & Southeast Asia.
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