Thank you for making a high quality hat for an adult with a small head! I did follow the advice of other respondents and 'sized up'; from the sizing chart I would have chosen XS (my head measurement is 20 3/4" or 53 cm) but I ordered a Small and it fits snugly. This is a meticulously constructed hat using excellent materials. I am delighted with my purchase. I grew up in the area where these items are manufactured, and the company is well known for superior standards, unique products, and reliable customer service.