# Area of a regular polygon

The number of square units it takes to completely fill a regular polygon. Four different ways to calculate the area are given, with a formula for each.
Try this Drag the orange dots on each vertex to resize the polygon. Alter the number of sides. The area will be continuously calculated.

The formulae below give the area of a regular polygon. Use the one that matches what you are given to start. They assume you know how many sides the polygon has. Most require a certain knowledge of trigonometry (not covered in this volume, but see Trigonometry Overview).

## 1. Given the length of a side.

By definition, all sides of a regular polygon are equal in length. If you know the length of one of the sides, the area is given by the formula: where
s  is the length of any side
n  is the number of sides
tan  is the tangent function calculated in degrees
(see Trigonometry Overview)

To see how this equation is derived, see Derivation of regular polygon area formula.

If you know the radius (distance from the center to a vertex, see figure above): where
n  is the number of sides
sin  is the sine function calculated in degrees
(see Trigonometry Overview)

To see how this equation is derived, see Derivation of regular polygon area formula.

## 3. Given the apothem (inradius)

If you know the apothem, or inradius, (the perpendicular distance from center to a side. See figure above), the area is given by: where
a is the length of the apothem (inradius)
n  is the number of sides
tan  is the tangent function calculated in degrees (see Trigonometry Overview).

To see how this equation is derived, see Derivation of regular polygon area formula.

## Irregular Polygons

Finding the area of an irregular polygon is trickier since there are no easy formulas. See Area of an Irregular Polygon