Determine the pipe's ID--the thickness of the pipe structure's wall. If unsure, ask a specialist. A retail pipe sales outfit might be able to assist you. The ID can also be referred to as the bore or standard. In the orifice beta ratio equation, the pipe ID will be represented by "d."
Determine the diameter of the pipe. If the diameter of the pipe is not known, calipers can be used to give a rough estimate for later equations. In the orifice beta ratio calculation, the diameter will be represented as "D."
Divide d by D, where "d" equals pipe ID and D equals the pipe diameter to get the orifice beta ratio, represented as beta. If the pipe ID is 2 and the pipe diameter is 8, the beta ratio would be 0.25 (2 / 8 = 0.25).