The way I use it, with the shelf on the bottom and no freezer compartment. I get a fermentation compartment that is 15.5" wide, 15.5" deep, and 19.5" tall. That works for 10 gallon Bayou Classic kettles and 7.9G buckets. That's all I have ever used to ferment. The kettle or bucket actually sit partly on that rear hump and the shelf the lines up with it.
Removing the bottom shelf and drawer and placing the fermenting vessel at the very bottom of the fridge allows for a fermenter that is 15.5" wide, 10.5" deep, and 27.5" tall. You loose about 5" of depth from the compressor hump. You can add maybe an 1.5-2" in depth by cutting out a portion of the inside door panel that holds the door bins.
Hope this helps. The measurements aren't precise, so give and take about 1/2". Sorry, I only had a tailor tape measure near by, but those are the measurements I got from the inside of this Frigidaire.