Varies based on pot diameter and number of jars in it as that affects water displacement. So you could do one 7" tall quart jar plus the two inches on water plus the 1" rack in a 10.5" deep pot with some splashing out while boiling.

But for multiple jars in general at least 16 inches deep. But you will still get some splash over at full boil. So 18" (23 quart stockpot) is much better. And be sure to allow height for the rack on the bottom as well when considering the height.

Dave

If you want to use a pot that is just a little too short try substituting a layer of canning jar rings on the bottom of the pot instead of a rack. I use a pot that is borderline in height so that is just enough extra room for me to use it, with some splash over. I just plan on mopping a little water off the stove. :)

even lower profile would be a pizza screen, available at restaurant supply stores. jars tend to move around sometimes without a full load, but they don't tip over, so that's what i use. so much easier than a traditional rack. the only problem is wedging the jar lifter between jars after processing. quarts should be no issue with that.