you mean the vertical bar for the handheld? unless children are using it, probably 24" is enough BUT you have to mount it way higher than you might think. test mount your shower head on the bar, and have someone hold it against the wall to see how high it needs to be. our contractor mounted ours crazy low while we werent there. from a distance it looks right... but its low when you stand by it. thankfully only i am the one to use it, my husband always uses the rainhead. (i use the rain head when i wash my hair, the hand held other wise.)

hoping when we go to sell our house no potential buyers will walk into the 5x8 shower to check it out... : (

24" is the size we have at my mothers house.

Get the 36 inch and mount it high enough that someone 6'6" can get under the spray head. The average height of typical Americans is growing.