I use this chart:
And if you want to back into the brannock device size and all you know is the inside length (assuming a normal toe shape), use can you this spreadsheet.
Edit: using this calc, your shoe comes out to a size 12.7, which = 13. Some other systems use 3/8 or 1/2" for the toe space. if you use half inch, you're dead on size 13.