In most standard shoe lines, the men's is built on a "D" last whereas the women's is built on a "B" last. (This has nothing to do with the idea that men prefer D's while women who run actually prefer B's) The width scale of foot sizing starts at AAA, and goes up to EEEE. {AAA, AA, A, B, C, D, E, EE, EEE, EEEE} Most companies just make a men's and a women's (D, B) and use length sizing to fill out the size line. Some companies (New Balance being one of the front runners in this regard) make
most of their models available in a variety of widths. Note most. You will likely never see a flat any wider than an EE, and if you do please let me know about it. Likewise, you will not likely see a motion control shoe on the AA side of the scale.
Most men's lines start at size 7 in length, while women's start closer to size 4 (not sure exactly how small they go - I've seen a 3 once). Therefore if you need a shoe smaller than a 7, there's a very good chance that all (or most) men's shoes will be too big.
What does this mean? Start by measuring your feet on a Brannock device (the metal foot measuring thingie they have at every shoe store in North America, but no-one ever uses) What does it say about your width? Now try on the men's 7, and the women's 8. Run in them. Go by feel from there.
The only difference you'll find aside from the fit (width) is the colour. Thankfully, shoe manufacturers are starting to realize that not all women want to run in pink and baby blue shoes, with sparkles.
<If you're gonna be dumb, you gotta be tough>
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