Jun 03, 2013

How big is a “U” when measuring rack size?

Rack heights are usually given in “U”s. For example, pretty much all the racks in our office are 42U. Since they are pretty much exactly the same height as me, I’ve always pretty much thought of it as U = You, but obviously this doesn’t work if you are shorter/taller than me. Is there a conversion to a standard unit of measurement?

Rack unit

"A rack unit, U or RU is a unit of measure that describes the height of equipment designed to mount in a 19-inch rack or a 23-inch rack. The 19-inch (482.6 mm) or 23-inch (584.2 mm) dimension refers to the width of the equipment mounting frame in the rack including the frame; the width of the equipment that can be mounted inside the rack is less). One rack unit is 1.75 inches (44.45 mm) high.

The size of a piece of rack-mounted equipment is frequently described as a number in "U". For example, one rack unit is often referred to as "1U", 2 rack units as "2U" and so on."

U = 1 3/4” or 44.45mm. So you and your racks are around 6’ tall (6’ 1 ½ “ to be precise). A 42U rack is a standard size. I have no idea where this standard of measurement originated, though.

Answer this