Ultra-Petite: 18.5" - 19.5" around the headPetite: 19.5" - 21" around the headPetite/Average: 20.75" - 21.25" around the headAverage: 21.25" - 22" around the headAverage/Large: 22" - 22.5" around the headLarge: 23" around the headExtra Large: 23.25" - 24" around the headFor a more secure fit, every wig has adjustable Velcro or Hook straps which can adjust up to 1" larger or smaller.The size of the wigs may be slightly different depending on the manufacturer of the wig.