I would agree that the Leica "Standard" or " A " is the smallest of Leicae.
As Brian noted, the -c and later screw-mounts are slightly larger - I measured the body on my III-f as being about 1/8" longer than my III or black II (D). I think I found this out when I was trying to put my IIIf into the case for my D... no go.
If you put an Elmar 35 mm lens (doesn't need to be pulled-out & locked like the 50) on a screw-mount, you have a very slim camera indeed !
I just got my first Contax RF ( IIIa), and my screw-mount Leicas are both smaller and noticeably lighter...
Wish we had a Leica dealer ( or any camera shop ) around here, with a case full of used gear...
Luddite Frank