5 fits well. Comfortable, easy-on fit immediately. But my biggest issue would be the comfort of the product, the material could be softer I can listen to music and read my book while my husband watches tv. The smallest size in Big Kid Under Armour slides that I could buy was a 4, otherwise I never would have ordered a 4 for my 7yr old to grow into. We did a two hour hike in El Yunque Rainforest and they held up to the test. Mackie make the most transparent audio gear and you shouldn?t pass up this introduction to what I believe is the best value for the highest quality headphones. finally lost 15 lbs and this snatches everything Not sure if its on mid volume or I need to keep switching bluetooth off when its not in use. I had some trouble figuring out how to put this together, as the only instructions were in the form of illustrations with no text.