Convert rack units to inches, millimeters, centimeters, or feet, or calculate rack units from a measured equipment height.

Convert rack units to nominal mounting height.

Nominal vertical rack space only. Chassis clearances, mounting holes, rails and the cabinet’s outside dimensions require manufacturer specifications.

Fractional U is allowed for dimensional conversion.

Rack Unit Height Formula

The following formula is used to calculate rack height from a given number of rack units (U).

h = 1.75 × n
  • Where h is the rack height (inches)
  • n is the total number of rack units (U)

To calculate the rack height in inches, multiply the number of rack units by 1.75 (since 1U = 1.75 inches).

What is a rack unit?

Definition:

A rack unit (U) is a nominal vertical mounting-space measure equal to 1.75 inches (1 3/4 inches), or 44.45 mm. It describes allocated rack space, such as 1U, 2U or 3U; it does not give the cabinet’s outside height. Actual chassis and faceplate dimensions allow for clearance. For a measured height, dividing by 44.45 mm gives the nominal U equivalent; rounding upward gives a whole-U envelope, not a guarantee of physical fit. Check the equipment’s specified U rating, rails and mounting compatibility.

How to calculate rack unit height?

Example Problem:

The following example outlines how to calculate a rack height from rack units.

First, determine the total number of rack units. In this case, the equipment is 3U tall, so the number of units is 3.

Next, the last and final step is to calculate the rack height using the formula above:

h = 1.75 × n

h = 1.75 × 3

h = 5.25 inches