1U, 2U, 3U, 4U, 5U, 6U, and 7U

Dell PowerEdge serversThe 1U, 2U, 3U, 4U, 5U, 6U and 7U are all different sized rackmount servers; the U following the number is short for unit. The number indicates the size of the rackmount, 1U being the smallest rackmount and 7U being the biggest rackmount. Below is a listing of each of the different units and their dimensions, although the Width and Height of a rackmount may be standard, the depth of a rackmount may change, as can be seen below. If your rackmount server is going to be placed in a constrained area, it's best to verify with the manufacturer of the rackmount what the exact dimensions are. The picture Courtesy of Dell Inc. shows some of the Dell PowerEdge servers and examples of different rackmount units.

Unit Dimension (W x H x D)
1U 19" x 1.75" x 17.7"
19" x 1.75" x 19.7"
19" x 1.75" x 21.5"
2U 19" x 3.5" x 17.7"
19" x 3.5" x 20.9"
19" x 3.5" x 24"
3U 17.1" x 5.1" x 25.5"
4U 19" x 7" x 17.8"
19" x 7" x 26.4"
5U 19" x 8.34" x 19.67"
19.1" x 8.75" x 26.4"
6U 19" x 10.5" x 19.5"
7U 17" x 12.2" x 19.8"

Most collocations and ISPs accept 1U, 2U or 5U chassis; however, it is still a good idea to check with whomever is planning to host your server to verify what they support and at what cost.

Also see: Chassis, Network terms