Chris
I can understand your confusion. It got me also when I first started with the instrument construction.
4/4 means that it is full size
4/4 Violin Boby legnth = 356mm
Violia for a 15 1/2" = 394mm
16 1/2" = 419mm
4/4 Cello = 755mm
I hope this helps. The 4/4 is the standard size for that class of bowed string instrument.
If you look at the 1/16 size fiddle the actual body legnth is about 8.5"
These are just the accepted standards.
Carl