Octagon Area Calculator

A = 2(1 + sqrt(2)) x 5^2 = 4.8284 x 25 = 120.71 square units. The perimeter is 40 and the apothem is approximately 6.04.

A = 2(1 + sqrt(2)) x s^2, where s is the side length. This simplifies to approximately 4.8284 x s^2. You can also use A = (1/2) x perimeter x apothem, which gives the same result.

A standard US stop sign is a regular octagon with sides of approximately 12.5 inches (31.75 cm). Its area is 2(1 + sqrt(2)) x 12.5^2 = 754 square inches (0.487 square meters). The total width across flats is about 30 inches.

Each interior angle of a regular octagon is 135 degrees. The sum of all interior angles is (8-2) x 180 = 1,080 degrees. Each exterior angle is 45 degrees (360/8).

A regular octagon with side s has a width (across flats) of s(1 + sqrt(2)). A circle with the same diameter has about 3.6% more area. The octagon captures 96.4% of the circumscribed circle area, making it a good approximation of a circle.

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