Circle: C=πd=2πr (d is the diameter, r is the radius, π).

Triangle: C=a+b+c (abc is the three sides of the triangle).

Quadrilateral: C=a+b+c+d (abcd is the side length of the quadrilateral).

Rectangle: C=2 (a+b) (a is length, b is width).

Square: C=4a (a is the length of the side of the square).

Polygon: C= sum of all sides.

Sector: C = 2R+ nπr ÷180 (n= center Angle) = 2R+kR (k= radian).

The circumference of the diamond C=4a (a is the length of the side of the diamond).

The circumference of the trapezoid C=a+b+c+d (abcd is the length of the four sides of the trapezoid).

The circumference of a positive n-sided shape C=na (a is the side length of a positive n-sided shape).

The above is a commonly used formula for calculating the circumference, which can be calculated according to different shapes.