How do I size critical equipment for a new data center?

Start from IT load and PUE target. Multiply IT load by PUE for total facility load; size UPS for IT load × redundancy factor; size generator for total facility load with motor-start margin (typically 1.25–1.5×); size transformer and switchgear for full facility kVA at PF 0.9.

What is the Uptime Institute Tier classification?

Tier I: single path, no redundancy. Tier II: redundant components, single path. Tier III: concurrently maintainable, multiple paths, one active. Tier IV: fault-tolerant, multiple active paths. Each tier targets specific availability (99.671% to 99.995%).

How much generator capacity do I need?

Size for full facility load (IT × PUE) plus an inrush margin of 25–50% for motor start, plus N+1 redundancy where required. For a 1 MW IT load at PUE 1.4, expect a 2.0–2.5 MW generator plant including margin.

What switchgear fault current rating should I specify?

Calculate prospective short-circuit current at the bus, then round up to the next IEC 61439 standard rating (e.g. 25, 36, 50, 65 kA). Coordinate with utility infeed and transformer impedance; consider current limiting if standard ratings are exceeded.

DC Critical Equipment Sizing

Size all critical power and cooling equipment for a new data center or an upgrade. Enter your design IT load and site parameters — get a complete equipment schedule.

New build — sizing from scratch

Load & Growth

Design IT load (kW)Total IT equipment power at full deployment

Growth headroom (%)Future capacity buffer applied to the design IT load before sizing (default 25%)

Required rack density (kW/rack)Sets the per-rack power requirement — determines how many racks the IT load can feed

Site Classification

Uptime Institute site tierDetermines availability requirements — Tier III is standard for commercial data centers

Target PUEPower Usage Effectiveness — ratio of total facility power to IT power. Best practice: 1.2–1.5

Utility supply voltageUsed to calculate switchgear fault current rating — 12.47 kV is typical for US colocation, 11 kV for UK/EU

Systems

Redundancy modelApplied to UPS, generator, transformer, and cooling — suggested default shown based on tier

Cooling strategyUsed to estimate rack density and PDU sizing

Enter your design parameters and click Calculate to generate the equipment schedule.

Published: April 2026 | Author: TriVolt Editorial Team | Standards: IEC 62040-3, ISO 8528, IEC 60076, ASHRAE TC 9.9, IEC 60364, IEC 61439, IEEE 485, Uptime Institute Tier Standard 2022

Sizing Methodology

All sizing figures are estimates based on standard industry sizing factors and should be treated as preliminary scoping values. Verify all equipment sizing with a licensed data center design engineer before procurement or construction.

UPS Capacity (IEC 62040-3, IEEE 446)

UPS kVA = (IT load × headroom factor) / (power factor × derating) × redundancy factor. Standard derating of 80% prevents operating at nameplate limit. Power factor 0.9. Redundancy factors: N=1.0×, N+1=1.25×, 2N=2.0×, 2N+1=2.1×.

Diesel Generator (ISO 8528, NFPA 110)

Generator kVA = (total facility load / generator power factor 0.8) × 1.25 motor-start margin × redundancy factor. Total facility load = IT load × PUE — generators must power cooling, lighting, and all other overhead, not just IT equipment. The 1.25 motor-start margin accounts for inrush current from chiller compressors and CRAC/CRAH fans starting simultaneously on generator pickup. The redundancy factor is then applied on top: for N+1 this results in a total installed kVA ≈ 1.95× the facility kW load, which is normal and correct. For example, a 3750 kW facility requires ~5860 kVA per generator unit (motor-start rated), and an N+1 system with 4 active units totals ~7500 kVA — spread across 5 × 1500 kVA generators.

MV/HV Transformer (IEC 60076)

Transformer kVA = generator kVA × 1.1. The 10% margin accounts for transformer impedance losses and provides capacity for harmonic currents from UPS rectifiers.

Cooling Plant (ASHRAE TC 9.9)

Cooling load kW = IT load × (PUE − 1). This is the non-IT overhead that must be removed as heat. Tons of Refrigeration (TR) = kW / 3.517. Redundancy factor applied per the selected model. ASHRAE TC 9.9 A1/A2 classes recommended for general server equipment.

PDU (IEC 60364)

Per-row PDU estimate based on rack density assumptions: air cooling 8 kW/rack, water-cooled 20 kW/rack, hybrid 12 kW/rack. Approximately 4 racks per row. Includes 1.2× safety factor and 0.9 power factor. Verify against actual rack layout.

Switchgear (IEC 61439 / IEEE C37)

Prospective short-circuit current: Isc = S / (√3 × U × Z%), where S = transformer kVA per unit, U = utility voltage in kV, Z% = 5% (standard transformer impedance). Rounded up to the nearest standard IEC rating: 16, 20, 25, 31.5, 40, 50, or 63 kA.

North American voltage classes: 4.16 kV and 12.47 kV are the most common utility distribution voltages for US data centers. Large colocation and hyperscale facilities often take 34.5 kV, 69 kV, or 115 kV directly from transmission and step down on-site. 12.47 kV is standard for facilities up to ~30 MW.

Battery Bank (IEEE 485)

Battery capacity for 10-minute bridging to generator: Ah = (UPS kVA × 0.9 PF × 10/60 h × 1000) / (192 V × 0.85 efficiency). Standard 192 V string (48 × 4 V VRLA cells). Specify extended runtime with a separate battery sizing calculation.

Redundancy Models (Uptime Institute Tier Standard, 2022)

Tier I (N): No redundancy — single path for power and cooling.
Tier II (N+1): At least one redundant component in each power and cooling path.
Tier III (N+1): Concurrently maintainable — multiple independent distribution paths, only one active.
Tier IV (2N): Fault-tolerant — two simultaneously active distribution paths, each independently sized for full load.

Frequently asked questions

How do I size critical equipment for a new data center?: Start from IT load and PUE target. Multiply IT load by PUE for total facility load; size UPS for IT load × redundancy factor; size generator for total facility load with motor-start margin (typically 1.25–1.5×); size transformer and switchgear for full facility kVA at PF 0.9.
What is the Uptime Institute Tier classification?: Tier I: single path, no redundancy. Tier II: redundant components, single path. Tier III: concurrently maintainable, multiple paths, one active. Tier IV: fault-tolerant, multiple active paths. Each tier targets specific availability (99.671% to 99.995%).
How much generator capacity do I need?: Size for full facility load (IT × PUE) plus an inrush margin of 25–50% for motor start, plus N+1 redundancy where required. For a 1 MW IT load at PUE 1.4, expect a 2.0–2.5 MW generator plant including margin.
What switchgear fault current rating should I specify?: Calculate prospective short-circuit current at the bus, then round up to the next IEC 61439 standard rating (e.g. 25, 36, 50, 65 kA). Coordinate with utility infeed and transformer impedance; consider current limiting if standard ratings are exceeded.

Also in Data Center

→ UPS Sizing Calculator — Size UPS capacity for N, N+1, and 2N redundancy configurations. Includes battery runtime estimation.
→ Power Chain Efficiency — Calculate overall power chain efficiency from utility through UPS, PDU, and cabling to IT equipment.
→ DC Cooling Load Calculator — Calculate the cooling capacity required for a given IT load and PUE target. Outputs in kW and Tons of Refrigeration.
→ DC Efficiency Audit — Enter PUE, power chain efficiency, cooling strategy, redundancy tier, and battery runtime to get an overall efficiency score with recommendations.