The most commonly used index in China is the FI value, also known as funnel-chest- index, which is measured as follows: the numerator is the transverse diameter of the anterior thoracic depression multiplied by the longitudinal diameter of the concave limit of the anterior thoracic area multiplied by the depth of the depression of the anterior thoracic area; the denominator is the length of the sternum multiplied by the transverse diameter of the thorax multiplied by the shortest distance from the sternal angle to the vertebral body. The calculated value measured by comparing the two reflects the severity of the funnel chest: less than 0.2 for mild, 0.2-0.3 for moderate depression, and 0.3 for severe depression. this is the measurement method we often refer to as the funnel chest index.