The size depends on the published length of the procedure turn and the altitude in three strata: <= 6000, >6000 to <=10000, and >10000 MSL. However, since most PT lengths are 10 nm, this effectively makes three commonly-used sizes.
However however, the largest one is used as a default UNLESS terrain or obstacles forces use of a smaller one. You will know this is the case if you see a PT with a MAXIMUM altitude charted at the PT fix. If not, then it was designed using the ">10000 MSL" size.
Assuming a 10-nm PT length, the "non-barb side" of the ">10000 MSL" PT still offers 6 nm of obstacle clearance from the centerline of the inbound course, with an additional 2-nm "buffer" width. And the total length of the PT from the fix outbound is 18 nm, again plus a 2-nm buffer area. So, yeah, most PT protected airspace is HUGE.