Headwear

A hat is a head covering. It may be worn for protection against the elements, for religious reasons (such as the Papa tiara), for safety, or as a fashion accessory.[1] In the past, hats were an indicator of social status. In the military, they denote rank and regiment.
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 an inch smaller than in the US.[2] Inches or centimeters may be used depending on the manufacturer. Felt hats can be stretched for a custom fit, and hard hats (such as Derbys and top hats) have a hard goss which can be melted to adjust size to a conformateur. Cheaper hats come in standard sizes, such as small, medium, large. Some hats, like baseball caps, are adjustable.
The general rule with removing hats in Western culture is that men do so frequently, while women do not, because they traditionally wore much more complex headgear, often requiring hatpins to hold down, making removal difficult. Men remove their hats when entering a Christian church, for example, and women do not.
An older custom requires women to cover their heads in church, often with a scarf, which is still followed in some places, such as Germany or southern America. Similarly, when being introduced or talking to a woman, a man would always remove his hat, and "tip" it (a brief touch to the brim) when briefly acknowledging a lady but not conversing with her, or upon meeting another man. Hats are removed by men when indoors, except in public or open places, such as stations, stairwells, lobbies or shops. Removing a hat can also be a sign of respect, so it was traditionally required in various other situations, such as public speaking outdoors.