Here is my spoke length calculator. It is designed to be as basic to use as possisble. It assumes you know why you need a certain length of spokes for your wheel, and that you know how to measure the non-spoke components of your future wheel. It also assumes you don't have very big spoke holes in your hub or anything like that.
Say, you must be a wheel builder to have wound up here. Nice to see you!
It is great for seeing how much the spoke length changes when you change one of the measurements by a millimeter or two. It is generally surprisingly small!
The math used to calculate spoke lengths in this program was taken from The Bicycle Wheel by Jobst Brandt, 3rd edition. Many wheels have been built using the calculations from this web page, and the math works as well here as is would fresh out of Jobst's book.
Updated November 28, 1997