NOTE: 98% of adults fit easily in our 2 sizes. To measure your head, circle the crown of your head with a string or dental floss (above eyebrows and ears.) Use a ruler to measure the string and compare to the above chart. Upon receiving your hat, loosen or tighten the sizing tape for a custom fit. Fit the hat slightly above eyebrows and ears to allow front and peripheral vision. Crown fabric should remain loose.