# What is the perimeter?

## What Does Perimeter Mean

We explain what a perimeter is, how it is calculated in different geometric figures and its applications in other disciplines.

## What is the perimeter?

In geometry, the perimeter is the sum of the lengths of the sides of any plane geometric figure . It is a key concept for mathematics , which together with area, which is close to it, is necessary to master in order to move towards more advanced mathematics such as algebra and trigonometry , since they allow the construction of polygons.

The word perimeter comes from ancient Greek (union of the voices peri , "all", and métron , "measure"), since the ancient Greek philosophers were the first to calculate it . The first thought of this type is attributed to the philosopher Archimedes (c. 287-212 BC).

The concept applies both to distance and length, or to the contour of figures; but in the case of circles it is called circumference . Half of the perimeter is called the semi-perimeter. The perimeter is represented by the letter P .

### Practical applications of the perimeter

The calculation of the perimeter has many practical applications, especially for architectural , engineering and construction work . For example, it can be used to calculate the edges or boundary of a space or an object, such as a terrain or a building.

If we want, for example, to place a fence around our garden, it will be necessary to calculate the perimeter of its surface, to know how many materials to buy and how to place them.

### Perimeter of a circle

The perimeter of a circle is called the circumference , and it is calculated by applying the following formula:

P = 2π. r = dπ

Where π is the mathematical constant equivalent to 3.14159…, r is the length of the radius of the circle and d is the length of the diameter of the circle. In the case of a semicircle, the formula will change to:

P = 2r + r. π = r (2 + π)

### Perimeter of a rectangle

In the case of a rectangle, you will not need to calculate the perimeter more than adding the lengths of its two long sides and its two short sides . That is, if the rectangle has two sides a (a1, a2) and two sides b (b1, b2), the perimeter will be calculated by adding a1 + a2 + b1 + b2.

### Perimeter of a square

The case of squares is identical to that of rectangles. In fact, in the case of regular polygons, whose sides measure exactly the same (like equilateral triangles), it will suffice to multiply the length of one side by the number of sides in the figure:

• Square. 4 identical sides measuring a, therefore P = ax 4 .
• Equilateral triangle. 3 identical sides that measure b, therefore P = bx 3 .

The same applies to other similar figures, regardless of their number of sides. On the other hand, for isosceles and scalene triangles each length of each side must be added.

### Perimeter of an irregular polygon

In the case of irregular polygons, that is, those that do not have identical sides and angles , it will suffice to add the measures of all the sides of the polygon , regardless of their shape. In case we do not have the measurements of some of these sides, the task will be complicated because we must first calculate them, but then we can proceed to add them without any difficulty.

Continue with: Polyhedra

Go up