Rack unit calculator
U
in
ft
cm

What is this calculator used for?

A rack unit (or U) is the standard terminology for describing sizes associated with 19 inch racking. Knowing how much rack unit space you require is incredibly important when installing 19 inch rack cabinets and enclosures. The unit calculator below can convert rack U's into cm, inches and feet, which makes it a very useful tool for any installer or musician who needs to know exactly what equipment to buy when building a 19 inch rack. Scroll down for a complete table of rack U-to-inch/feet/cm values.

What is a “U” or “Rack Unit”?

A rack unit (abbreviated as U, less commonly seen as RU) is a unit of measurement applied to equipment racks and the servers, disk drives and other devices that they contain. One U is 1.75 inches (44.45mm); the standard rack, at 19 inches, is 42U.

Rack servers and other hardware designed to be rack-mounted are manufactured in multiples of 1.75 inches and specified in multiples of rack units, usually 1U, 2U, 3U or 4U. Racks are designed to hold equipment of those sizes. The holes in the mounting flanges of racks are arranged in groups of three, and that three-hole grouping is also called a rack unit.

Rack units for equipment is considered maximum dimensions. In practice, devices are often made slightly smaller than the specified U value to allow a little space. A device specified as 2U, for example, may in reality measure 3.44 inches in height, rather than the 3.5 inch multiple of 1.75.

Rack unit conversion table

Rack Units
Height (in)
Height (ft)
Height (cm)
1U 1.75″ 0.15′ 4.4 cm
2U 3.5″ 0.29′ 8.9 cm
3U 5.25″ 0.44′ 13.3 cm
4U 7″ 0.58′ 17.8 cm
5U 8.75″ 0.73′ 22.2 cm
6U 10.5″ 0.88′ 26.7 cm
7U 12.25″ 1.02′ 31.1 cm
8U 14″ 1.17′ 35.6 cm
9U 15.75″ 1.31′ 40 cm
10U 17.5″ 1.46′ 44.5 cm
11U 19.25″ 1.6′ 48.9 cm
12U 21″ 1.75′ 53.3 cm
13U 22.75″ 1.9′ 57.8 cm
14U 24.5″ 2.04′ 62.2 cm
15U 26.25″ 2.19′ 66.7 cm
16U 28″ 2.33′ 71.1 cm
17U 29.75″ 2.48′ 75.6 cm
18U 31.5″ 2.63′ 80 cm
19U 33.25″ 2.77′ 84.5 cm
20U 35″ 2.92′ 88.9 cm
21U 36.75″ 3.06′ 93.3 cm
22U 38.5″ 3.21′ 97.8 cm
23U 40.25″ 3.35′ 102.2 cm
24U 42″ 3.5′ 106.7 cm
25U 43.75″ 3.65′ 111.1 cm
26U 45.5″ 3.79′ 115.6 cm
27U 47.25″ 3.94′ 120 cm
28U 49″ 4.08′ 124.5 cm
29U 50.75″ 4.23′ 128.9 cm
30U 52.5″ 4.38′ 133.4 cm
31U 54.25″ 4.52′ 137.8 cm
32U 56″ 4.67′ 142.2 cm
33U 57.75″ 4.81′ 146.7 cm
34U 59.5″ 4.96′ 151.1 cm
35U 61.25″ 5.1′ 155.6 cm
36U 63″ 5.25′ 160 cm
37U 64.75″ 5.4′ 164.5 cm
38U 66.5″ 5.54′ 168.9 cm
39U 68.25″ 5.69′ 173.4 cm
40U 70″ 5.83′ 177.8 cm
41U 71.75″ 5.98′ 182.2 cm
42U 73.5″ 6.13′ 186.7 cm
43U 75.25″ 6.27′ 191.1 cm
44U 77″ 6.42′ 195.6 cm
45U 78.75″ 6.56′ 200 cm
46U 80.5″ 6.71′ 204.5 cm
47U 82.25″ 6.85′ 208.9 cm
48U 84″ 7′ 213.4 cm