Measure it with a Brannock device

Brannock devices have been part of your life, I bet. 

These metal measuring devices are standard fare in any shoe store.  Yes, the funny looking metal tool with adjustable slides and many numbers.  They are accurate at telling the shoe salesperson your true shoe size.

 Its inventor, Charles Brannock, was born in Syracuse, New York in 1903. He grew up in the family retail show business.