I need to get some extra spokes for a customer. Is there a way to measure without pulling the spoke?
Thanks!

Tom- Yes, but there's a greater "fudge/judgement" range than if the spoke was in hand. I simply place the end point of a ruler against the spoke still in the hub, as close to the spoke's elbow (or head if straight) as you can and make a mental note of any "correction factor" if the ruler end can't line up well. Run the ruler parallel to the spoke in play and note the rim's inner point. Now add up that sort of length you got with any head end correction factor and also add the rim's "thickness". For spokes that interlace the others (the usual case) I'll add a mm or two to account for the spoke not traveling a true straight line.

If possible, I like to place the estimated length spoke against the still in the wheel one to try to confirm the length is close enough to work, before I leave on the tour... Andy

I suppose one could do a spoke length calculation if the rim, spoke pattern and hubs are known.

Next to ERD, spoke offset is the most critical dimension to get right on straight pull hubs. That adds a level of complexity to measuring the hub dimensions. When replacing one spoke, I find removing one to measure is the most expedient method.

Thanks for your replies!
I decided to just pull one from the front wheel. Git a measurement and can now "estimate " the rear because I can "see" where to measure.