Size: For athletic shoes I typically wear a men's 11.5 since women's 12.5 are hard to come by. For casual/dress shoes I wear a women's 12. With these sandals I could use the extra half size but since Chaco doesn't do have sizes I think they'll work fine (definitely better than a men's 12 which is huge on my foot).
Purpose: I bought these sandals for an upcoming trip to Mali, West Africa. I was told that for everyday and hiking, sandals are the way to go because you can just kick the sand out rather than having to constantly take your shoe off and dump it out.