Just go to a legit shoe store like AE, get measured on the brannock. Try on some shoes, remember the size and the model of those that fit you well, do further research on how that particular model fits and size your desired boots accordingly. Profit?
I`d rather not go by how some forum seller measured it. Hell even the online stockists would have varying measurements and every pair have their slight variances to account for... just too many factors. Last thing you want to be is in the wrong size when it comes to boots. These are not as forgiving unlike sneakers