What is a
server rack?

Definition: what is a server rack?

A server rack — also called a rack, 19-inch rack or server cabinet — is a standardised metal enclosure for housing IT components such as servers, switches, patch panels, storage systems and network devices. Standardisation via the 19-inch standard (DIN 41494) ensures that devices from all manufacturers fit into any standard-compliant server rack.

The difference from a conventional electrical enclosure: a server rack is designed for IT equipment — with perforated ventilation for active cooling, cable management for structured cabling and a high load capacity for heavy servers. ZPAS electrical enclosures for industrial controls follow different standards and design principles.

What do 19-inch and U mean?

The 19-inch standard defines the mounting width: exactly 482.6 mm (19 inches), measured across the mounting flanges. All standardised IT devices (servers, switches, patch panels etc.) use this width — enabling compatibility regardless of manufacturer.

The rack unit (U) — also written RU — measures 44.45 mm. A 1U device is 44.45 mm high, a 2U device 88.9 mm, and so on. The most common server rack sizes:

• 12–22 U – Small racks for network distribution, branch and very small sites
• 32–36 U – Medium-sized racks for server rooms
• 42 U – Industry standard. 42 × 44.45 mm = 1,866 mm mounting height in the rack. The most common format in data centres worldwide.
• 45 U – For maximum capacity with the same external dimensions. Available as ZPAS Z-SERVER.
• 47 U – Highest density. Special design for very high capacity requirements. Available as ZPAS Z-SERVER.

Rule of thumb: 42 U is the market standard. 45 or 47 U is worthwhile when mounting density is to be maximised and floor space minimised.

How many U does my server rack need?

The U requirement is the sum of the rack units of all installed devices plus a reserve for later expansion. Calculation: add up the device U, allow for cable management and PDU, then add a 20–30 % reserve — and round up to the next common size. A server rack with 42 U offers 42 × 44.45 mm = 1,866 mm of usable mounting height.

Typical heights of common components:

Component	Typical height
Rack server (1U version)	1 U = 44.45 mm
Server with more drives / GPU server	2–4 U
Switch, router, firewall	1–2 U
Patch panel, 24 ports	1 U
Horizontal cable management	1 U per patch panel level
UPS (rack version)	2–6 U plus battery modules
Power strip (PDU)	1 U horizontal, 0 U when mounted vertically

Example calculation: 6 servers at 2 U (12 U) + 2 switches at 1 U (2 U) + 3 patch panels at 1 U (3 U) + 3 cable guides at 1 U (3 U) + UPS 4 U + PDU 1 U = 25 U. With a 30 % reserve this comes to around 33 U — so the right size is a 42 U cabinet.

Smaller sites manage with 18–24 U, server rooms with 32–42 U. Where floor space is tight, the Z-SERVER with 45 or 47 U provides additional mounting height on the same footprint; the SZB IT covers the range from 18 to 47 U. You can try out all sizes in the server rack configurator.

What depth does a server rack need?

The cabinet depth is determined by the deepest installed device — not by the average. Calculate: device depth + approx. 50–100 mm clearance in front of the profiles + 150–250 mm of connection and cable space behind the device. A server 750 mm deep therefore needs a cabinet depth of around 1,000 mm.

Depth	Typical application
600 mm	Pure network distribution: patch panels, small switches, wall-mounted distributors
800 mm	Network cabinet with switches, routers and short appliances
1,000 mm	Standard server rack for rack servers up to approx. 750 mm device depth
1,200 mm	Deep servers, GPU systems, side cable ducts, rear-door heat exchangers

Rule of thumb: 600 and 800 mm are network depths, 1,000 and 1,200 mm are server depths. The ZPAS Z-SERVER is available in 1,000 and 1,200 mm, the SZB IT in 600 to 1,200 mm. If rear-door cooling or dense rear cabling is planned, choose 1,200 mm from the outset — depth cannot be added later. The series at a glance: 19-inch server racks and network cabinets.

Load capacity: what matters?

The load capacity of a server rack is particularly critical in high-performance environments. Modern servers — especially for AI and high-performance computing — can weigh 30–50 kg per device on their own. A fully populated 42 U rack quickly adds up to a tonne or more.

• Standard racks – Typically 600–1,000 kg load capacity. Sufficient for medium-sized IT environments.
• ZPAS SZB IT – up to 1,500 kg static load capacity. Universal cabinet for network and server equipment, 18–47 U, 600/800 mm wide, 600–1,200 mm deep.
• ZPAS Z-SERVER on levelling feet – 1,600 kg static load capacity, load evenly distributed. For heavily loaded data centre environments.
• ZPAS Z-SERVER without levelling feet – up to 2,000 kg, standing directly on the floor. For GPU servers, AI racks and extreme high-load applications.

Example calculation: 20 rack servers at 30 kg add up to 600 kg, a rack UPS with batteries accounts for 150–250 kg, plus switches, cables and accessories. A densely populated 42 U rack therefore realistically weighs 800–1,200 kg; GPU racks with servers of 40–50 kg each exceed 1,500 kg. The design rule is: the rated load capacity of the cabinet should be at least 25 % above the calculated equipment load.

Important: the stated load capacity must refer to the base frame — not just the rails. With heavy servers, also check the floor load capacity of the server room (with raised floors, the point load per floor tile also applies). For complete data centre solutions with cold aisle containment and rack cooling: → ZPAS data centre & server room solutions.

Server rack vs. network cabinet: what is the difference?

The terms are often used interchangeably — but there is a functional difference:

• Server rack – For heavy, high-performance servers. High load capacity, deep design (typically 1,000–1,200 mm), strong ventilation for high heat dissipation. ZPAS Z-SERVER: 42/45/47 U, 600/800 mm wide, 1,600 kg static on levelling feet, 2,000 kg without.
• Network cabinet – For switches, patch panels, routers, KVM systems. Lower depth (600–800 mm is sufficient), lower load capacity requirements, often a glass door for a clear view. ZPAS SZB IT (up to 1,500 kg, door opening up to 270°), DSR IT — for small amounts of equipment on the wall: Z-BOX and Z-CUBE (6–21 U), in open, secured rooms: open racks SRD/SRX. Overview and selection criteria: → Network cabinet.

In short: both follow the 19-inch standard and do not differ in mounting width, but in depth, load capacity and ventilation. In practice, a deep server rack (1,000 mm+) is recommended for a mixed rack with servers and network equipment, as servers typically need more depth than switches. You can put together series, dimensions, doors and cooling in the server rack configurator.

Cooling in the server rack: perforation and active systems

Servers generate considerable power loss — and it must be removed reliably. Cooling starts with the rack itself:

Perforated doors

The perforated doors of the ZPAS Z-SERVER achieve 86 % perforation with an open cross-section of 80 %. This is crucial for the natural front-to-back airflow — the basic principle of server room cooling. The larger the open cross-section, the lower the air resistance and the cooler the operation.

Active rack cooling

• BWC-DX2 – ZPAS rear-door heat exchanger with up to 11.2 kW cooling capacity. Mounted directly on the rear door of the rack, it cools the exhaust air right at the source.
• KWT in-row cooling – For high-load environments. ZPAS KWT systems with 12.3–37.7 kW cooling capacity, installed directly between the racks.
• Cold aisle/hot aisle containment – Separates cold and warm air at room level. Reduces cooling energy demand by up to 40 %. Recommended from 5–6 racks or from 5 kW per rack.

For AI racks and GPU servers with 30–100 kW of power loss per rack: → high-density cooling systems in the ZPAS data centre range. Device selection and sizing for IT racks in detail: server rack cooling.

How do I calculate the waste heat in a server rack?

For IT equipment, the simplified rule is: all the electrical power drawn is converted into heat. The power loss in the rack therefore equals the sum of the actual power consumption of all devices — 1 kW of power consumption means 1 kW of waste heat.

Calculation in three steps

• 1. Add up the power consumption – Use the actual consumption per device, not the rated power of the power supply. Power supplies are usually oversized; the actual consumption is typically 40–60 % of the power supply rating.
• 2. Add UPS losses – Rack UPS and PDU additionally generate about 3–6 % of the power passing through them as heat.
• 3. Add a reserve – The cooling capacity should be 10–20 % above the calculated power loss to cover load peaks and later expansion.

Example: 10 servers with 400 W actual consumption each = 4,000 W, two switches at 150 W = 300 W, UPS losses around 200 W. Total: 4.5 kW of waste heat per rack. With a 15 % reserve, the cooling requirement is around 5.2 kW.

Which cooling system suits which load?

Power loss per rack	Typical solution
up to approx. 1.5 kW	Perforated doors and filter fans (ZPAS LV) with exhaust filter (GV)
approx. 1.5–5 kW	Room air conditioning with organised cold/warm air routing
from approx. 5 kW	Rack-based cooling, e.g. rear-door heat exchanger BWC-DX2 with up to 11.2 kW
from approx. 12 kW	In-row cooling KWT (12.3–37.7 kW) with cold aisle/hot aisle containment

Standards and form factors

Relevant standards for server racks:

• DIN 41494 – Defines the 19-inch mounting width and the rack unit (U = 44.45 mm). The basis of all compatible IT devices.
• EN 60529 / IP standard – Degree of protection. In server rooms, IP 20 is typically sufficient (no dust or water protection required). For installation sites with higher requirements, the Z-SERVER is available up to IP 54.
• IEC 62208 – For empty enclosures in low-voltage applications.

ZPAS Z-SERVER and SZB IT racks are manufactured to DIN 41494 and EN 60529. CE declarations of conformity are available in the downloads section.

When is a server rack direct from the manufacturer worthwhile?

Buying directly from the manufacturer pays off especially when:

• High load capacity is required: for AI servers, GPU racks and heavy hardware, the ZPAS Z-SERVER offers a static load of 1,600 kg on levelling feet and 2,000 kg without — design and verification agreed directly with the manufacturer.
• Larger quantities: for rollouts across several sites, direct project support from the manufacturer pays off — uniform configuration and coordinated delivery dates.
• Individual adaptations: special colours, special depths, integrated cooling or customer-specific equipment are nothing unusual at ZPAS.
• Complete data centre solution: racks, cooling, cold aisle containment and UPS from a single source — short coordination paths, one point of responsibility.

Frequently asked questions — server rack

What is the difference between a server rack and a network cabinet?

Both follow the 19-inch standard and do not differ in mounting width, but in depth, load capacity and ventilation. A server rack is designed for heavy servers: 1,000 to 1,200 mm deep, high load capacity and highly perforated doors for heat dissipation. A network cabinet houses switches, patch panels and routers, manages with a depth of 600 to 800 mm and has lower load capacity requirements. For mixed equipment, a server rack with a depth of 1,000 mm or more is recommended.

How many rack units does a server rack have?

One rack unit (U) equals 44.45 mm. The market standard is 42 U, which corresponds to 1,866 mm of usable mounting height; the ZPAS Z-SERVER is also available with 45 and 47 U, the SZB IT from 18 to 47 U. To determine your requirement, add up the U of all devices, allow for cable management and PDU and add a reserve of 20 to 30 per cent. Example: 25 U of equipment plus reserve gives around 33 U, so a 42 U cabinet is the right fit.

How deep should a server rack be?

The depth is determined by the deepest installed device: device depth plus 50 to 100 mm clearance in front of the profiles plus 150 to 250 mm of connection and cable space behind. 600 and 800 mm are network depths for patch panels and switches, 1,000 and 1,200 mm are server depths. A server 750 mm deep needs a cabinet depth of around 1,000 mm. The ZPAS Z-SERVER is available in 1,000 and 1,200 mm, the SZB IT from 600 to 1,200 mm.

How much weight can a server rack carry?

Standard racks typically carry 600 to 1,000 kg. The ZPAS SZB IT is designed for up to 1,500 kg, the Z-SERVER for a static load of 1,600 kg on levelling feet and 2,000 kg without levelling feet. A densely populated 42 U rack realistically weighs 800 to 1,200 kg, GPU racks exceed 1,500 kg. The rated load capacity should be at least 25 per cent above the calculated equipment load; the floor load capacity of the server room must also be checked.

How do I calculate the cooling capacity for a server rack?

All the electrical power drawn by the IT is converted into heat: 1 kW of power consumption means 1 kW of waste heat. Add up the actual consumption of all devices (not the rated power of the power supplies), add 3 to 6 per cent for UPS losses and a 10 to 20 per cent reserve. Example: 4.5 kW of waste heat results in a cooling requirement of around 5.2 kW. Up to 1.5 kW, filter fans are sufficient; from around 5 kW, rack-based cooling makes sense. The cooling and heating capacity calculator does the calculation for you.