Finding the Right Shoe Size for Women's Styles

Apologies if this has come up before; I’m fairly certain it has. Jessica keeps pestering me to buy her shoes. I’ve put it off because I don’t want people watching me try them on or holding them against my feet for a side-by-side look. Does anyone know where I can find a sizing chart to help me determine the correct size? I’m usually a men’s 10, so if someone could just tell me what that converts to in women’s sizes directly.