Felt top hats is a head covering. It may be worn for protection against the elements, for religious reasons, for safety, or as a fashion accessory. In the past, hats were an indicator of social status.
Felt hats 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. Hat sizes are determined by measuring the circumference of a person's head. In the UK, an equivalent hat size is an eighth an inch smaller than in the US. Inches or centimeters may be used depending on the manufacturer.