Spoke length for 24X4 wheel and Nexus 3 speed?

[Donovan]

Building a Choppers US 24X4 (the double bump one) wheel with a nexus 3 speed. Does anybody know the spoke size I'd use for a 3 cross or a radial lacing?

 

[expjawa]

You'd need to get some dimension information for both the hub and the rim, but there are online calculators that can answer your question. This is one I've used - its actually pretty straightforward, just read the tutorial:
www.bikeschool.com/tools/spoke-length-calculator

I also have an app for that on my phone. I usually use both to make sure that I'm getting consistent results.