Unless your fingers are really small I would venture to guess that you would need the large pick. I don't consider my fingers all that large and there was no way I could get them into the small size. The medium felt uncomfortably tight. The large picks are not all that large and I wouldn't be surprised if some people would possibly want an XL size.

I did find the Fred Kelly web page and under "contact" he gives a phone number.   Think its a tole free number but not sure...

http://www.fredkellypicks.com/

I bought three of the finger picks because I often use three fingers when playing the classical guitar and the large size fits all three fingers nicely without slipping.

Cap't Bob