Measure your head size with a tape measure going around the head behind the ears, from the nape of the neck to the hairline. If you don't have a tape measure, use a length of string and measure the string. Most wigs are made in the average size. Petite and large head size wigs are identified in the style specifications.

Wigs are typically available in up to six sizes:

Petite/Petite -- 20¾"
Petite -- 21"
Petite/Average -- 21¼"
Average -- 21½"
Average/Large -- 22½"
Large -- 23"