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