of rack units would imply. Thus, a 1U front panel would be 1+23/32 in tall. If n is number of rack units, the ideal formula for panel height is ''h'' {{= 1.750n - 0.031}} for calculating in inches, and ''h'' {{= 44.45n - 0.79}} for calculating in millimetres. Manufacturing allows for dimensions with less precision.

The 19-inch rack format with rack units of 1.75 in was established as a standard by AT&T around 1922 in order to reduce the space required for repeater and termination equipment