Mine vary and inch or two, to the height of the horse. All of mine are low enough that the horse can easily hang it's neck and head over the door and look out on what's going on. I do, however, have dutch-doors on the stalls which are next to the cross-tie area, so that they can be closed when a horse has to be tied for clipping or whatever.
With out checking with enough people we built our stalls and doors about 40". If we keep the bedding deep enough it is down to 36". This appears to be to tall for ours as we only have 1 horse over 30 1/2". The stalls are too high for them to see over very well. I am looking for ideas to modify doors so they can at least put heads out to see who else is looking.
I guess I should add that my stall walls at 4 feet are not solid. THey can see through them and nose each other. If I had solid walls I would cut my doors down a bit or have them be wire so they could see out.
The solid section (2" x 6" boards) of our stall walls is 30" tall. We then have about 28" of heavy duty wire panel on top of that sandwiched 1 1/2" down in between the top board and the posts, so it's flush against the board. It's also sandwiched on another 2" x 6" on the very top for extra strength. The panels have 4" x 4" holes and are 5' tall x 20' long. One panel cut in half lengthwise and in the middle vertically will do (4) 10" stall walls! The sections end up 9' 10" x 28". Since I sandwich and anchor them in the center of my 4' X 4' uprights, they don't HAVE to be 10' long.
Our gates are just round pipe gates. I do have my store mechanic/welder working on some of the gates, welding the same heavyweight panels on the gates to prevent the mane rubbing issue
All of our horses can see the entire length of the barn and our feisty stallions have just had to get over it and learn to live next door to each other
I do have 1 bad boy stall that has a 36" solid wall section with the same panel height on top.
Edited to add- this is 1 side of the barn only, that has 5 stalls, 3 eight feet wide and 2 twelve feet wide (can be divided with portable panels to make two 6' x 10' stalls each).
All of my stalls are 10' deep and there is a 10' aisle.
The other side (1 eight foot stall, 1 ten foot stall and 1 twelve foot stall) has "temporary" permanent dividing walls made from portable corral panels. They are VERY strong, but can be removed fairly quickly if I need to bring one of the big horses or larger ponies in for some reason. Rainey (16h) will foal in my indoor round pen area next year (30' x 30') *if* I haven't already moved to the new farm <g>.