Straight Bisected Octagon

Calculations at a straight bisected octagon, a regular octagon halved in the middle of two parallel sides. This results in a convex hexagon with one long and two short sides, as well as three sides of the original octagon. The height of this form is half the long side b. Another method of bisecting a regular octagon to create two equal parts is the diagonally bisected octagon.
Enter one value and choose the number of decimal places. Then click Calculate.

	Octagon side (a):
	Long side (b):
	Short side (c):
	Perimeter (p):
	Area (A):
	Round to   0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15   decimal places.

Lengths and perimeter have the same unit (e.g. meter), the area has this unit squared (e.g. square meter).

Dividing the octagon eliminates half of the original vertices and adds two new ones, resulting in 8/2+2=6 vertices, thereby creating a hexagon. These two new vertices form right angles and lie along the hexagon's longest side. The other four vertices have angles of 135 degrees, corresponding to the angles of a regular octagon. Of the six sides, three are sides of the original octagon, two short sides are half that length, and the long side is the medium diagonal of that octagon.
The bisected octagon has a single axis of symmetry running centrally and perpendicularly through the longest side and the opposite side. It possesses no other symmetries. It has no circumcircle and no incircle.

Larger structures, such as buildings, often feature a cross-section that tapers, or narrows, towards the top. There are structural reasons for this, among others. A bisected octagon of this or a similar type can serve as a building's cross-section. This configuration offers the benefits of a pitched roof while saving roofing material and maximizing the usable space in the upper apartment. This is known as a mansard flat roof. While not very common, this roof shape does occur, though the upper angles usually differ.

Calculation of area and other dimensions: straight bisected octagon

Last updated on 07/13/2026. Author: Jürgen Kummer

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