How do I calculate the area of a regular polygon?

Formula: Area = (1/2) × Perimeter × Apothem = (1/2) × n × s × a, where n = number of sides, s = side length, a = apothem (distance from center to midpoint of a side). Alternative using only side length: Area = (n × s²) / (4 × tan(π/n)). The apothem: a = s / (2 × tan(π/n)). Examples: equilateral triangle (n=3): Area = (√3/4) × s². s = 10: area = 43.3. Square (n=4): Area = s². s = 10: area = 100. Regular hexagon (n=6): Area = (3√3/2) × s². s = 10: area = 259.8. Regular octagon (n=8): Area = 2(1+√2) × s². s = 10: area = 482.8. As n increases, the polygon approaches a circle: a regular 100-gon with side length 1 has an area very close to πr² where r is its circumradius. This is actually how Archimedes first estimated π — by computing areas of 96-sided polygons inscribed in and circumscribed around a circle.

What is the apothem and how do I find it?

The apothem is the perpendicular distance from the center of a regular polygon to the midpoint of any side. It's the 'inradius' — the radius of the largest circle that fits inside the polygon. Finding the apothem: from side length (s): a = s / (2 × tan(π/n)). From circumradius (R, center to vertex): a = R × cos(π/n). From area (A): a = 2A / (n × s). Relationship between apothem and circumradius: a = R × cos(π/n), and R = s / (2 × sin(π/n)). Examples: for a regular hexagon with s = 6: apothem = 6 / (2 × tan(30°)) = 6 / (2 × 0.5774) = 5.196 cm. Circumradius = 6 / (2 × sin(30°)) = 6 / 1 = 6 cm (for a regular hexagon, R = s). For a regular pentagon with s = 8: apothem = 8 / (2 × tan(36°)) = 8 / 1.4531 = 5.506 cm. Practical uses: the apothem determines the maximum diameter of a circle that fits inside the polygon (important for engineering — bolt patterns, nut sizes, pipe fittings). A hex nut with 'across flats' measurement = 2 × apothem, 'across corners' = 2 × circumradius.

What is the effect of increasing the number of sides on the area of a regular polygon?

As the number of sides increases, the area of the regular polygon also increases, given a constant side length. For example, a regular hexagon with a side length of 5 units has an area of approximately 64.95 square units, while a regular octagon with the same side length has an area of around 82.82 square units. This is because the formula for the area of a regular polygon, Area = (n * s^2) / (4 * tan(180/n)), shows that area is directly proportional to the number of sides, n.

How does the side length impact the area and perimeter of a regular polygon?

The side length has a significant impact on both the area and perimeter of a regular polygon. If the side length is doubled, the area increases by a factor of 4, since Area = (n * s^2) / (4 * tan(180/n)) is proportional to the square of the side length. For instance, if the side length of a regular pentagon is increased from 4 units to 8 units, its area increases from approximately 27.53 square units to 109.96 square units, and its perimeter increases from 20 units to 40 units.

Can the area of a regular polygon be used to determine its side length or number of sides?

Yes, the area of a regular polygon can be used to determine its side length or number of sides, given one of the other variables. By rearranging the formula for the area of a regular polygon, Area = (n * s^2) / (4 * tan(180/n)), we can solve for the side length, s, or the number of sides, n. For example, if the area of a regular polygon is 50 square units and it has 6 sides, we can solve for the side length: 50 = (6 * s^2) / (4 * tan(180/6)), yielding a side length of approximately 4.04 units.

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n= number of sidess= side lengthR= circumradiusa= apothem

Area from side length

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Area from circumradius

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n= number of sides

s= side length

R= circumradius

a= apothem

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Reviewed September 2026

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Area from side length

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