Hard to say, it seems to depend on the weather and the make of shoes! And my right foot is shorter than my left foot but also wider...... so a shoe that fits my left won't always fit my right. Oh and which country I'm shopping in seems to make a difference.
Basically, I try on at least three different sizes of shoe until I find the right one for that day and that design! Nothing if not awkward :)
I take a 7 1/2 (Australia) but usually buy an 8 as half sizes are so rarely available these days. It's funny as my mother and I were the same height (mum is in her 80's now and has shortened) but her shoe size is much smaller - a five.
I wear an Australian 11 in a woman's shoe. I often buy men's sneakers as they tend to be wider and therefore more comfortable for me. Then it is usually a size 10 but in some brands a 9 is okay. I recall Mum taking me shopping for shoes when I was 12 and the sales woman looking at my feet and saying, 'My, she HAS got big feet.'