I'm terribly spoiled, I have a 7 1/2' high locker, 2 1/2 feet wide, 2 1/2' deep. All boarders at our facility have the same, except for the one with two horses has a corner one which is double the size. There's a top shelf, and a bottom shelf (which still leaves room for tall boots), which maximizes space, plus two bridle hooks on the door, and one on each side of the interior. One saddle rack, but room for two if you needed them.

Where my little guy is, they are set up to handle babies, so I keep his 'stuff' in the trunk of my car. Babies don't need a lot of equipment, however!