I wanted to buy some new slippers today but they only came in small medium or large in our local supermarket. We’ll that was strange. Feet come in lots of sizes and not averages. I had socks and shoes on which I didn’t want to take off but I remembered something from reading art books. Your forearm is the same length as your foot! The medium ones were the closest in length to my forearm and seemed to match the length of my shoes so I bought some. On wearing them they are a smidgen too small, but if I had bought the large ones they would have been like boats! Supermarkets? Not good to just sell three sizes!