How to Size Rack Space and Power for Co-location

The most common co-location mistake is ordering “one full rack” and then discovering the contracted power cannot support the equipment you planned to put in it. Data centres sell space and power separately, and power is usually the tighter limit.

Step 1: list the equipment

For every server, storage array, switch and firewall, note the height in rack units (U) and the measured or realistic power draw — not the nameplate rating of the power supply, which is a maximum and can be two to three times higher than typical use.

Step 2: add it up in kW

Total the realistic draw and add 20–30% headroom. A rack of modern 1U and 2U servers can easily reach 5–8 kW; GPU servers can exceed 10 kW per rack. Many facilities price standard racks at a few kW, with higher densities charged extra or requiring special cooling.

Step 3: plan redundancy

Ask for A+B power feeds and connect dual power supplies to different feeds. Remember that each feed must be able to carry the full load on its own if the other fails.

Step 4: cabling and networking

• Reserve space for patch panels, top-of-rack switches and cable management.
• Decide which carriers, internet exchanges and cloud on-ramps you need cross-connects to.
• Label everything and keep an up-to-date rack elevation drawing.

Step 5: growth

Estimate growth over the contract term. It is far easier to reserve adjacent space or extra power on day one than to split equipment across rows later.

Our engineers size, design and build co-location racks every week. Explore our co-location service or share your equipment list for a free sizing.