Originally Posted by JohnDThompson

Spoke length is a function of rim diameter, hub diameter, number of spokes, and how many times (if any) they cross other spokes between the hub and the rim:



Source: Sutherland's 4th Edition



Needless to say, these days most people use a spreadsheet or on-line calculator:

https://www.google.com/search?q=spok...hrome&ie=UTF-8