Our visors, beanies, and under helmet caps are one size fits most. The Sweatvac Performance Race Hat is available in two sizes—Medium/Large, and Small/Medium. All Race Hats have an adjustable strap in the back. M/L hats are 21.5 inches in circumference when the strap is adjusted normally, can expand up to 23 inches, and tighten to 20 inches. S/M hats are 20.5 inches when adjusted normally, can expand up to 23 inches, and tighten to 19.5 inches.