Scale is based on 6' tall person. How this came to be, is beyond me.
12" = 1/6, 1" = 1'
6" = 1/12, 1/2" = 1'
4" = 1/18, 1/3" = 1'
3" = 1/24, 1/4" = 1'
2" = 1/48, 1/6" = 1'
1/72, 1/48 and 1/32 are the most popular military aircraft scales, but as you can see, 1/32 is in the middle, so it starts getting into inches and fractions per foot (i.e. something like 2.6" = 1/32).
Military armor and figures use a different scale based on mm, so they get weird mesurements like 1/35.
I believe most SS models are considered to be roughly 1/24, but I don't know if the model makers stayed to any particular scale.
-Fred