The server cabinets are measured in U. Each U is equal to 44.45mm (1.7 inches) which represents the height of the units within a standard 19-inch cabinet. The 19inchs server cabinet is commonly used in telecommunication and computing industry. There are many server cabinets ranges for the units which are from 6U to 47U, and often can come in two types as well; wall mounted and floor. The wall mounted server cabinets will be up to 6U to 18U and for the floor cabinets it will be anything above 18U.
Remember: This unit of measure only measures the height not the width of the server cabinets or its depth, which can vary widely.