I wear a 10 W women's.

In shoes I have to get a 9.0 or 9.5 in men's.
But these were 8 M in men's.
I have worn one shoe long ago that was an 8 M men's.
I wear a 42 euro.

Shoe contours are called "lasts". Some run large, some small.

The salesgirl at the store said that the men's Medium is wider than the Women's W as a rule.
Sometimes Famous Footwear has a lot of selection in 10 W for me in the women's section. Yesterday it was dismal...forcing me to the Men's. The men's shoes seem to be a little bit higher, have thicker softer tongues, and provide more support, in general. With Unisex these days, many styles look very much alike. I prefer nylon uppers over leather, because the leather can be too stiff and push down on the top of the balls of my feet when flexing and walking and aggravate the sesamoids over time. The nylon is cooler wearing. I removed the insert they came with and put in a Doctor Scholl's gel insert...that was much much better too.

I had to try on alot of shoes...it wore me out, and the squeezing worked up the pain levels in my feet all day. But I am happy with what I finally found.