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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”.

Practical uses

Perimeter and area play a great role in today’s world. Perimeter is used in calculating the border of an object such as a yard or flowerbed when a fence or other border is being installed around the edges. Area is used when all the area inside of a perimeter is being covered with something, such as a yard being covered with sod or fertilizer.

Formulas

Polygons

As a general rule, the perimeter of a polygon can always be calculated by adding all the length of the sides together.
So, the formula for triangles is <math>P=a+b+c</math>, where <math>a</math>, <math>b</math> and <math>c</math> stand for each side of it. For quadrilaterals the equation is <math>P=a+b+c+d</math>. For equilateral polygons, <math>P=na</math>, where n is the number of sides and a is the measure of the side.

Circles

For circles the equation is

<math>

 P = 2 \cdot \pi \cdot r

</math>
or

<math>

 P = d \cdot \pi

</math>

• <math>P</math> stands for the perimeter,
• <math>r</math> stands for the radius
• <math>\pi</math> is the mathematical constant pi (<math>\pi=3.14159265…</math>)
• <math>d</math> stands for the circle’s diameter (twice the radius of a circle)

(The dot means multiply or times)

In General

If r is considered to be the distance from the centre of a regular polygon to one of its vertices (or in the case of a circle, the radius), the following holds true:

<math>P = \frac{dA}{dr}</math>

• <math>P</math> stands for the perimeter,
• <math>r</math> stands for the radius
• <math>A</math> stands for the area

See also

• Isoperimetric Theorem
• Circumference
• Pythagorean Theorem
• Wetted perimeter

External links