We size boots by the gender-neutral European sizes, because the changes-by-sex-of-wearer North American sizing is confusing to read on a tag. (Womens 10.5, Men’s 9.25? Men’s 7, women’s 8.5? Makes your eyes cross, especially as everyone is pretty much looking for the same tough, functional boots.)
In the store, on the boot racks, we have this wee chart hanging everywhere:
All humans: Pick your Euro size, and then shop with a fast glance at the size sticker on the sole of the boot. So easy!