Unified Code for Units of Measure
The Unified Code for Units of Measure (the UCUM) is a system of codes for unambiguously representing measurement units to both humans and machines.
The code set includes all units defined in ISO 1000, ISO 2955-1983, ANSI X3.50-1986, HL7 and ENV 12435, but explicitly and verifiably addresses the naming conflicts and ambiguities in those standards to resolve them. It provides for representations of units in 7 bit ASCII for machine to machine communication, with unambiguous mapping between case-sensitive and case-insensitive representations.
A reference open-source implementation as a Java applet is available.