What length driveshaft do I need?

I have a 96 xj with a crysler 8.25 rear axle np231. I recently changed transmissions from aw4 to an ax15 5 speed . The parts jeep had a Dana 35. The driveshaft from the ax15 is longer but of corse doesn't fit. I'm trying to find the length to know what I'm looking for. Having a hard time finding the numbers

Find a drive-line shop near you and have your cut to length.

Follow this link, click on the XJ section. It'll tell you everything you need to know on how to measure.

http://www.4xshaft.com/

Assuming rear since you mention the 8.25 and D35. Rear driveshaft length for an XJ is determined by four factors:

manual or automatic
2wd or 4wd
95- or 96+ transfer case output shaft style
D35 or D44/8.25 rear axle

You need a driveshaft from a 96+, ax15, 8.25.