Mine are odd shaped. I only have 2 stalls. 10'8 x 12. I am going to extend one stall to about 10'8 x 17 for my stallion because he stays in his stall ( by his choice ) and that will give him more space but will reduce my goat to about a 4 x 10'8. But she is a pigmy so that will be plenty big enough for her.
I have boarded at 3 commercial barns and one private barn at this point in my life and all of them had 10 x 12 stalls. This seems to be the norm here. There are barns with 10 x 10 stalls as well (too small for my big horses, imo). The biggest horse I've owned was a 16'3" TB--he lived outside anyway (much happier outside).
I don't have any stalls at my house yet, but would probably build 2 10 x 12 and the rest 12 x 12 with the option to take out a divider in the 10 x 12's if I needed a large stall for breeding/confinement/some yet unknown huge horse. I keep everyone turned out outside as much as possible anyway.
12x12 in the barn we have now - would not want anything smaller but considering 12x14 for the next barn.
Even though you have to initially use a bit more bedding, I think the horses are neater in a larger stall. Most of our guys have a bathroom corner and the rest stays pretty clean, and then there is Travis, our little tornado. Smallest horse in the barn and he stall is a constant wreck.
Perfect timing on this question. We are about to build a barn. I originally was thinking 10x10 but got to thinking that might be too small. Two of my horses are 14.2 and one might be 15hh if his toes are long so 10x10 will probably be fine. Besides, they will only be locked in for feeding.
My home stalls are 10x12. And I'm not sure why, but often people look in my stalls and say, "Wow, these are huge!" And they're not huge. But maybe some folks are more used to solid side walls or a dropped ceiling and my stalls just look bigger due to grilled side walls or open ceiling?
Around here stalls are almost always 10x10, 10x12 or 12x12. And that's mostly because either those are the sizes pre-fab stalls and stall kits are made. Or because that's the sizes boards are sold in already or it matches up with supports in a barn.
There is a glorious old barn 2 towns over that has hand-made 15x15 stalls. They look fantastic! Those would be nice to have for some horses...but not all. Like my younger horse is the world's filthiest stall pig most of the time and that would just give him a whole lot more space and bedding to destroy, LOL!
Mine work great for me...and were just fine when my mare was in them and she was 17hh and long. But if I had to re-do my barn interior...I'd splurge on the uber-awesome stall systems that not only have side walls that can un-pin and swing flat to the back wall to make an instant double stall...but they make them on sliders too so you can pull a couple pins and move the wall where you want it. Want to change the 12x12? Slide it 2 feet in either direction. Since my barn is only a 4 stall it wouldn't be uber-expensive to swap out to more expensive stalls and I may do that some day. I can put it on my huge list of "Someday" projects, LOL!
You jump in the saddle,
Hold onto the bridle!
Jump in the line!
The last side of our barn that I added has 12 x16s. There're far easier to clean than the one 10x12, and three 12x12s we have on the other side of the aisle. There is no stirring in the larger stalls. The horses pick a spot and use it over there, since they have plenty of room. I even tried the horses who made a mess in the small stalls in the big stalls, and they kept the big ones clean with no stirring.
If I built another barn from scratch, they'd all be 12x16s. We started with a small 2-stall shedrow, and did several additions, including the 15' wide aiselway, and complete other side with 12x16s. Four of the 12x16s convert into two 24x16 foaling stalls, which we liked when we used them too.
Mine are 14' x 14', but my biggest horse is 15.2 hands, most are under 14.3 hands.
We may be building some more and in that one barn, they fit best, as we think right now, 12' x 16'.
Not quite sure, will have to see about that.
A friend just built a new barn and he made his 24' x 12' for now, each with a 24' x 48' run.
If he needs more space later, he can cut some in half.