If I'm a size 9 in women's shoes sizes and a 7 in men's, then what boot size for women am I?

I need help! I'm going to a concert and I love Dr.Martens, the only thing is, is that I'm buying them for the first time and I have no clue on what my BOOT size is, not shoes sizes. I know that by memoire! XD Please help and if you don't have nothing nice to say, then please, don't say nothing at all!