If you hover over the "Sizes Available" with your mouse, a tap will appear and provide you with the correct numeric sizing. 41 (US: M Size 9, F 10) or 40 (US: M Size 8, F 9) should work for you depending on your sex. Have a great day
There are size conversion charts on the website. It matters whether you are talking men's or women's size 9. These slippers seem to run true to size, but they slip off (my feet) easily, unless I have on socks. Hope that helps....