The calculation formula of arc length is a mathematical formula, L=n×π×r/ 180, L = α× r ... where N is the degree of central angle (angle system), R is the radius, L is the arc length of central angle, and α is the degree of central angle (arc system).

If it is known that it cuts the cone along a generatrix of the cone and the intersection of the side surface and the bottom circle, the plane development diagram of the cone can be obtained. It consists of a circle and a sector whose radius is the length of the generatrix of the cone, and its arc length is equal to the circumference of the circle at the bottom of the cone. This sector is also called the side spread of the cone.