He wears a boys size 2 or 2 1/2. I wanted a slipper to wear while walking around on the hardwood floors but also didn?t want a full slipper since I live in California and my feet would get too hot. Their website which allows you to "personalize" your Cardo unit is very quirky. Fits well, good protection for my AirPods. Doors broken. Its a great shelf at a good price. The velcro straps hold it tight and one of them I use to hold the smith machine bar clamp from catching during donkey leg press. Not sure if I need a wider size? I hope to be able to break them in. These use S/M/L type sizing instead of shoe sizing. With a good fitting ear sleeve these are comfortable for multi-hour wearing.