Area of a regular octagon calculator
Enter the dimensions of a regular octagon and read off its area, its perimeter and the quantities that follow from them.
Area
77.254 834m²
- Perimeter
- 32
- Across the flats
- 9.656 854 2
- Across the corners
- 10.452 504
Show the working
- Side = 4
- Area = 2 * (1 + sqrt(2)) * 4^2 = 77.2548
- Perimeter = 8 * 4 = 32
- Across the flats = 4 * (1 + sqrt(2)) = 9.656 85
- Across the corners = 4 * sqrt(4 + 2*sqrt(2)) = 10.4525
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- area = 2(1 + sqrt 2) s^2
- across flats = s(1 + sqrt 2)
Lengths are entered in metres by default; switch any field to feet, inches or millimetres and the conversion is exact.