You can find a lot of useful information on ground forces here hxxp: www. aurorawiki. pentarch. org/index. php?title=Ground_forces#Special_Operations_units. As it states, divisions (the two low tech ones, which you probably want to upgrade rather than moving around) have a size of 50, and troop transport bays have a rating of 5 (small troop transport bays have a rating of 1) so you'll need 10 troop transport bays to move one low-tech division.
If you're referring instead to Division HQs, a Division HQ can fit 4 Battalion HQs, which each can command 4 Battalions, for a total of 21 units = 105 size, = 21 troop transport bays at max (not counting construction brigades, which you probably won't want to put in a battalion HQ anyway).