Based on the measurements given for this item, I ordered the XL, though my head is pretty small. MISTAKE! I should have gone with my gut and ordered the small. BUT I expressed my reluctance in a chat and was basically assured the sizing for this product was perhaps different from other sizing, like for my small mask frame. So duped twice. The smallest size they offer is for a measurement, chin to top of head, of 6 inches! Really? Who has a head that size? No adult I can think of. I will rate again once I return it. I will rate it very low again if I end up paying for shipping.