If a client's head measures 22 inches, the wig size that should be selected is typically a size "Medium". This is because a head circumference of 22 inches falls within the standard range for a medium-sized wig, which typically ranges from 21.5 to 22.5 inches in circumference. However, it's important to note that wig sizes can vary by manufacturer and style, so it's always a good idea to check the specific sizing chart provided by the manufacturer or consult with a professional wig fitter to ensure the best fit.