There is no standard sizing for reusable and disposable ear plugs, and
most are one-size-fits-all.
However, some brands come in small, medium and large -- a good starting
point if you know that your ears are on the large or small side. Try a
variety of earplugs until you have a good idea of your ear and ear canal
size. As a heads-up for women, most earplugs are sized for men, so you're
more likely to get a good fit from a smaller size.