Use the Brannock!
You think you know your shoe size, but I think you don’t.
Every shoe is different. Not just brand to brand, but model to model, the relationship between the size of the shoe and the number printed inside is variable. This is doubly true for shoes lasted in one set of sizes (Euro, or UK for example) and sold in another.
But that’s no excuse.
Most men picked a shoe size when they were about 16, and have stuck with it ever since. They mostly picked that shoe size based on a hyper-cushioned pair of sneakers, built to accomodate feet of nearly every length and width. That number in your head might or might not actually have anything to do with the size of your foot.
This is the part where I make an admission. I’ve been buying size 12 shoes since I was a teenager. In fact, in some athletic shoes, I need a 13. No amount of heel slipping was going to convert me to anything different from trusty old 12D.
A few years ago, I started to realize that maybe I had narrow feet. Then one day I happened to try on a 12C. “Hmm,” I thought. “Feels pretty good.”
Then one day I bought some loafers at the thrift store. I tried them on before I looked at their size. They fit great. 11 1/2 B.
So today, I put my foot in the Brannock Foot Measuring Device. It’s true. I’m not a 12D. I’m an 11 1/2 B. Maybe a 12 B. My shoe buying (especially online) will never be the same.
So get yourself to a real shoe store, and put your foot in the Brannock. Who knows what you might learn.