The question I am most frequently asked when I sell shoes -- when I forget to put it in the measurements -- is for the *inside* measurement from toe to heel, along the inner sole. I also give the *inside* measurement from side to side at the widest part of the inner sole.
The next most important measurement is the heel height and the height of boots.
For good 'measure' I give the measurements along the bottom of the sole, from toe to heel and side to side at the widest part of the sole.
Lynne