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/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/Large | 7 1/2 and up | 7 1/2 and up | 23 1/2 - 25 | 60 - 63 | Large and tall men with hair |