How high is the birthday hat?

The birthday hat is made of thin cardboard, with a bottom radius of 9 cm and a height of 12 cm.

The size of the hat is determined according to the head circumference. To measure the head circumference, you can use a tape measure to measure the head (the most prominent part of the forehead and back of the head) for one week, and the tape measure can rotate slightly. At this time, the head circumference is the size of the head circumference, so as to judge the appropriate hat size standard.

Generally speaking, the size of hats in China starts from size 46, with children's hats 46-56, adults' hats 55-60 and oversize hats over 60. The arithmetic difference between numbers is 1cm, forming a series. Generally, the cap size of adult men is 55-56, that of children is 50-55, and that of baby hat is 42-46.