In the 1920’s, Charles Brannock invented a measuring device, which bears his name and is still used today in most retail shoe stores.
According to the Brannock Device, men’s shoe sizes are one size larger than women’s. For example a men’s size 9 shoe would fit a woman’s size 10 foot. The size increments for both are 1/3″ difference between each size. So if you need to go up or down a half size, you’re only changing the size by 1/6″. Not nearly as much as most of us think.
There is also a nifty conversion chart on the Brannock Device’s website which differentiates different sizing systems, including children and European sizes as well.
Here’s the link http://brannock.com/cgi-bin/start.cgi/brannock/charts.html