Shoe sizes can vary from brand to brand. In general there’s about a 1.5 size difference between men's and women's shoes. For instance an 8.5 in women’s shoes, is usually a men's size 7.
Many Etsy sellers offer sizing charts and other sizing information, and it’s a good idea to measure your feet before purchasing. Tape a sheet of paper on the floor and trace your foot, keeping the pen vertical. Repeat on the other foot, and measure the longest and widest part of your feet.