Perimeter

The perimeter is the distance around a given two-dimensional object. The word perimeter is a Greek root meaning measure around, or literally "around measure." Perimeter can be calculated for any two dimensional object, with the right formula.

Practical Uses
The calculation of perimeter and area have many practical applications. The formula for calculating perimeter can be used to determine the total length of the border of an object, such as a yard or flowerbed, when a fence or other border is being installed. The formula for area is used when the area inside a perimeter is being covered with something, such as a yard being covered with sod or fertilizer.

Formulas
As a general rule, the perimeter of a polygon can always be calculated by adding all the length of the sides together.

Circles: For circles the equation is:

$$P=2 \pi r\,$$

Where $$r$$ is the radius and $$\pi$$ is the mathematical constant, or about 3.14. (An equivalent formula is $$P= \pi d$$, where $$d$$ is the diameter).

Area: The equation for the area of a circle is:

$$A= \pi r^2\,$$

Where $$r$$ is the radius and $$\pi$$ is about 3.14. Pi comes from the equation c/d, which is the circumference of a circle divided by the diameter.

Triangles: For triangles the equation for the perimeter is the sum of the lengths of the three sides:

$$P=Side1 + Side2 + Side3\,$$

The area of a triangle can be calculated by the equation:

$$A= \frac {1}{2}bh\,$$

Where $$b$$ is the length of the base and $$h$$ is the height of the triangle.

Quadrilaterals: For quadrilaterals the equation for perimeter is simply the sum of the lengths of the four sides:

$$P=Side1 + Side2 + Side3 + Side4\,$$