Polygon Calculator

Use this calculator to determine the radius or sides of regular polygons. Measurements in inches. Examples:

Pour a 5 sided concrete pad with a diameter of 120" (10'). Enter the diameter of 120". Build forms cut to 36^o and 70 - 9/16 long on the short (inside) of the form.
Build a 8 sided redwood planter with 24" long sides (outside). The angle of the boards will be 22.5^o. The resulting planter will have a diameter of 62-11/16"
How big of a square sheet is needed to layout a hexagon with 24" sides? Enter the side length of 24". The resulting diameter (48") is the size of the square sheet.
I want to add on to a building 1/2 of a hexagon shaped room. The width of the opening is 8' (96"). Enter a diameter of 96"). The resulting sides would be 48" long (inside measurement).
To build a 8 sided gazebo that is 12' (144") across on the outside, cut the forms at 22.5^o. The inside of the slab forms would be 55-1/8" long. The outside of the plates would be 55-1/8" long.

Miter Angle is the angle to cut boards to be fit in to the polygon shape.

Rise/12": Use with a framing square to layout the miter angle. Similar to rafter angles.

Side Length is the length of a side for a specific diameter (entered). For concrete forms this will be the short (interior) side.

Diameter is the diameter of the circle that circumscribes the polygon. Based on the entered side length.

Apothem is the distance from the center of the polygon to the midpoint of a side. Based on the entered side length.

Formulae Used:

Angle = 360 / sides

Miter Angle = Angle / 2

Rise = run / tan(90-miter angle)

Side = Diameter x sin(180 / number of sides)

Diameter = side / sin(180 / umber of sides)