Ladies that are a solid US size 9......

I am between a 8.5 and 9 though I tend to wear 9 for flats and boots; 8.5 for heels. I usualy start with a 39.5 for flats. It has worked for all brands I've tried from Ferragamo to Taryn Rose for me. The exception has been MBMJ shoes which I need sometimes need a 40.
 
I also am a solid US 9 and usually go with EU 40, Chloes, Dior, Marni, Dolce and Gabbana. Prada/Miu Miu I can wear their 39, 40 is too big. I'm always afraid to buy flats online because they fit so differently than the heels/boots I usually buy.