Spoke length calculation

R = Effective Rim Diameter (ERD)

F = Hub Flange Diameter

h = Hub Drilling Diameter

H = Center-to-flange Spacing

C = Spoke Crossing Pattern (# of crosses)

S = Number of Spokes

 

Take those and run them through the equation in the picture.

 

Note that for most rear hubs, you will need different length spokes for each side of the wheel (i.e., for each hub flange). This is due to the different center to flange spacing.

Done