Generally 24", but you could go to 30".

Use your ruler to measure your existing closets and the garments that hang in them.

HI -- I just measured mine and they are 26 inches deep and the sleeves get caught in the door and I have to tuck the bigger coat sleeves in . So Pamela suggested 30 inches and that or a little more would be the best . A lot of the new builds I see now are only doing 24 inch deep closets and that is mostly to cut costs and doesn't make sense for winter coats etc. So if you have the room I say ... the bigger the better !!

Agree, 30 inches deep would be more spacious for winter coats.