The optimum height of the pillow should be about 8~ 15cm. The height of the pillow can be determined according to your shoulder width and sleeping habits. The supine can choose a pillow with a high fist, and the lateral sleeper can choose a pillow with a shoulder width and a shoulder length. It can be calculated by the formula (shoulder width-head width) ÷2. Men should choose a higher pillow because of their wider shoulders, while women should choose a lower pillow.