Resource
The rack sizing guide.
Size a server rack the right way — by U-space, power draw, cooling load and weight — then match the UPS that keeps it online.
Resource
Size a server rack the right way — by U-space, power draw, cooling load and weight — then match the UPS that keeps it online.
A rack has to fit your equipment physically, power it reliably, and shed the heat it produces — all within its weight limit. Get those four right and the UPS and cooling choices fall into place. Here is the method, step by step.
Add the U height of every device (servers, switches, PDUs, KVM), then add spare U for cable management and growth. Cabinets are commonly 42U, 45U or 48U.
Confirm equipment depth fits the cabinet (deep servers need 1000–1200 mm cabinets) and that the total loaded weight is within the rack and floor rating.
Sum the power (W) of all equipment. This figure drives everything downstream — PDU rating, UPS size and cooling. Light racks draw 2–5 kW; dense racks 15–30 kW+.
Choose PDUs rated above the rack draw, and use dual A+B feeds for redundancy. Balance load across phases on three-phase PDUs.
Nearly all rack power becomes heat, so a 6 kW rack needs ~6 kW of cooling. Use hot-aisle/cold-aisle containment above ~5 kW per rack.
Size the UPS to the rack draw plus 20–25% headroom, then pick runtime. Single racks suit compact UPS; rooms move to three-phase or modular systems.
Rack units. One U is 44.45 mm (1.75 in). Total the U of every device, then leave spare U — a common rule is to plan for no more than 70–80% fill so there is room for airflow, cable managers and growth.
Depth. Match cabinet depth to your deepest device plus cabling room. Shallow network cabinets suit switches; deep servers and GPU nodes need 1000–1200 mm cabinets.
Weight. A full rack can exceed 800 kg. Check the cabinet's static load rating and the floor loading, place heavy gear (UPS, batteries, chassis) low, and never overload a raised floor without confirming its rating.
Add the wattage of everything in the rack. This is the number that sizes the PDU, the UPS and the cooling. Densities vary widely — a patching rack may draw under 2 kW, while an AI/GPU rack can exceed 30 kW.
Select PDUs rated comfortably above the rack draw, and feed critical racks from two independent paths (A+B) so either can fail without dropping the load. Balance the load across phases on three-phase PDUs.
Electrical power in equals heat out: a 6 kW rack rejects about 6 kW of heat. Your cooling must remove at least that much. Above roughly 5 kW per rack, hot-aisle/cold-aisle containment keeps supply and return air separated and the equipment within temperature.
Rule of thumb: 1 kW of IT load ≈ 1 kW of heat to remove ≈ about 3,412 BTU/hr of cooling.
Say a 42U rack is 70% filled with servers and switches drawing 6 kW total, on dual feeds, and you want 10 minutes of ride-through to a generator.
FAQ
One rack unit (1U) is 44.45 mm of vertical mounting height. Add up the U height of every device, then add spare U for growth, cable managers and PDUs. Common cabinets are 42U, 45U and 48U tall.
Add the power draw of all equipment in the rack. Light IT racks draw 2–5 kW, typical enterprise racks 5–10 kW, and high-density or AI racks 15–30 kW or more. This total drives PDU, UPS and cooling sizing.
Almost all electrical power a rack consumes becomes heat, so a 6 kW rack rejects roughly 6 kW of heat. Cooling must remove at least that, with hot-aisle/cold-aisle containment recommended above about 5 kW per rack.
Size the UPS to the rack's total power draw plus 20–25% headroom, then choose runtime. A single 5–10 kW rack often suits a single-phase 6–10 kVA UPS; multiple racks or a room usually move to a three-phase or modular UPS.
Loaded racks are heavy — often 500–1,000 kg or more. Confirm the cabinet's static load rating and the floor loading, especially on raised floors, and distribute heavy equipment low in the rack.
Talk to an engineer
Tell us your rack count, power per rack and runtime — we'll size the UPS, batteries and redundancy and share pricing.