Measure around the forehead, just above the ears, and around the hair in the back to determine head size. If your measurement falls on a size cut off guideline, we recommend that you order the smaller size as there is a bit of stretch in the fleece material. 

SleepPhones® & RunPhones® Size Hat Size (US) Hat Size (UK) Inches cm Estimate
Extra Small Up to 6 3/4 Up to 6 3/4 20 - 21 3/8 51 - 54 Petite women with short hair
Medium (one size fits most) 6 7/8 - 7 3/8 6 7/8 - 7 3/8 21 1/2 - 23 3/8 55 - 59 Nearly everyone
Extra Large 7 1/2 and up 7 1/2 and up 23 1/2 - 25 60 - 63 Large and tall men with hair