Hi, the best I can do is give you the measurements of one of my 3d printed 1/35 scale ones (bought at Shapeways).
Height : 22 mm ( excluding the feet)
Length : 24 mm
Width : 17 mm
I have to rectify my mistake here, the midget sub is actually a "Molch" (Salamander). Quite a few of these were also found in the Dutch town of Den Helder after the liberation in 1945.The midget sub was of the "Seehund" type