The formula for calculating the circumference of a circle is = 3. 14× diameter.

The circumference of a rectangle = (length+width) ×2 C=(a+b)×2.

Circumference of a square = side length ×4 C=4a

Circumference = π× diameter = 2×π× radius C= πd = 2πr

Area of rectangle = length× width S=ab

Area of a square = side length × side length S=axa= a2

Area of triangle = base × height ÷2 S=ah÷2.

Area of parallelogram = base × height S=ah

Area and perimeter

If it is a triangle with the same area, the perimeter of an equilateral triangle is the shortest; If it is a quadrilateral with the same area, the perimeter of the square is the shortest; If pentagons with the same area are used, the perimeter of regular pentagons is the shortest; If you use any polygon with the same area, the circumference of a regular circle is the shortest.

Perimeter can only be used on two-dimensional figures (planes and surfaces), and three-dimensional figures (solids) such as cylinders, cones and spheres can't express their boundary size by perimeter, but by total surface area.

Total surface area = the total area of all sides of a solid.