Hat sizes are determined by measuring the circumference of a person's head about 1/2 inch (1.3 cm) above the ears and dividing by pi. In the UK, an equivalent hat size is an eighth of an inch smaller than in the US. Inches or centimeters may be used depending on the manufacturer. Fleece hat can be stretched for a custom fit. Cheaper hats come in standard sizes, such as small, medium, large. Some hats, like baseball caps, are adjustable.