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Getting a 19 Inch Rack Panel Right the First Time

Updated September 25, 2026

A rack panel is geometrically simple and full of ways to be slightly wrong. Getting it right is almost entirely a matter of copying the standard accurately and then adding the clearances that the standard does not mention.

The numbers

The governing standard is EIA-310, in its various revisions. The figures that matter to a panel designer:

Dimension	Value
Nominal panel width	482.6 mm (19 in)
Practical machined width	482.0 to 482.6 mm
Rack unit (U) pitch	44.45 mm (1.75 in)
Panel height formula	h = 44.45n minus 0.79 mm
1U panel height	43.66 mm
2U panel height	88.11 mm
3U panel height	132.56 mm
4U panel height	177.01 mm
5U panel height	221.46 mm
6U panel height	265.91 mm
Horizontal hole centre spacing	465.1 mm (18.312 in)
Hole distance from panel centreline	232.55 mm each side
Clearance hole diameter	7.14 mm (0.281 in), plus or minus 0.08

Rather than work these out by hand, the rack panel calculator gives the height, width and slot positions for any rack unit count, plus a drawing note you can paste.

The hole pattern within a U follows the standard’s 15.875 / 15.875 / 12.7 mm vertical sequence, which is why the holes are not evenly spaced. For a 1U panel, two holes per side positioned symmetrically about the panel centre is the safe, universally compatible arrangement.

Slots, not holes

Round holes at nominal positions work when everything is at nominal. In a real cabinet with real rails, they frequently do not.

Use vertical slots: roughly 7 mm wide by 10 to 12 mm tall, with the centre at the standard position. The installer gets a couple of millimetres of vertical adjustment and the panel goes in without a fight. Almost all commercial rack gear does this.

For a cosmetic panel, a countersink or a counterbore around the slot lets the screw head sit flush or recessed, which looks far better than a washer standing proud.

Thickness and stiffness

2 mm aluminum: the minimum for a 1U panel. Lighter gear only.
3 mm: the common choice for 1U and 2U.
5 to 10 mm: high end and boutique look. Also what you need if the panel carries the weight of a transformer or a front mounted heavy assembly.

A 19 inch panel is a long thin beam. At 3U and above in thin material it will bow visibly when the four corner screws are tightened. Either go thicker, add a stiffening return on the rear face or add centre mounting points.

The clearances nobody puts on the drawing

These are the ones that cause a panel to arrive perfect and not fit.

Handle envelope. Rack handles project forward and sideways. Check they clear the rail and the cabinet door.
Screw head clearance. A screw head plus a cup washer needs about 3 mm of flat panel around the slot. A chamfer or a feature too close to the slot means the screw cannot seat.
Chassis to panel offset. The panel is wider than the chassis behind it. Make sure the chassis body clears the rack rails, which project inward from the panel mounting face.
Panel to panel gap in a stack. The 0.79 mm subtraction gives roughly 0.4 mm above and below each panel. Any feature that projects beyond the panel face, a lip, a bent edge, a proud fastener, eats into that and causes binding in a full rack.
Ventilation. A solid 19 inch panel in front of a warm chassis blocks front to back airflow. If the design needs intake at the front, it has to come through the panel or around it.

Cosmetic considerations specific to rack panels

A rack panel is seen from directly in front, in a stack, usually under harsh overhead light. That is an unforgiving viewing condition.

Brush direction is horizontal on almost all rack gear, running the long axis of the panel. It makes the panel look wider and it matches nearly everything the panel will sit next to.
The slot edges are visible. Deburr and break them properly, and decide whether the counterbore is brushed with the face or left as machined.
Screws are part of the design. Black anodized cup head screws on a black panel, or exposed stainless as a deliberate contrast. Choose rather than default.
Long panels show bow. A 3U panel that bows 1 mm is invisible on a bench and obvious in a rack next to a flat one.

A drawing checklist

Width 482.0 to 482.6, with a tolerance you have chosen
Height per the formula for your U count, tolerance plus or minus 0.2
Slot positions dimensioned from the panel centreline, not from an edge
Slot size and any counterbore or countersink
Thickness and flatness callout over the full length
Brush or blast direction with an arrow
Which faces are cosmetic
Cutout positions for connectors and controls, dimensioned from the same datum as the slots
Edge breaks on every visible edge
Fastener specification if the panel ships with screws

Frequently asked questions

Why is a 1U panel 44.45 mm in some places and 43.66 mm in others?

44.45 mm is the rack unit pitch, the vertical space one U occupies. The panel itself is made slightly shorter so that units stack without binding. The standard formula is h = 44.45n minus 0.79 mm, which gives 43.66 mm for 1U. Making the panel the full 44.45 guarantees a stack that will not fit.

Should the panel be 482.6 mm exactly?

482.6 mm (19 inches) is the nominal. Machine it slightly under, typically 482.0 to 482.6, because a panel at exact nominal will bind in a cabinet whose opening is at the low end of its own tolerance. A little under is invisible and always fits.

Do I need slots instead of round holes?

Slots are strongly preferred. Rack rail hole spacing varies within the standard and threaded rails in older cabinets vary more. A vertical slot of about 7 by 10 mm gives the installer the movement needed to get all four screws in without forcing anything.

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Keep reading

This guide is part of Audio Chassis Manufacturing: The Whole Picture, one of four sections in the guide library.