Veelhoekig Prieeldak & Sparren Calculator

Enter the number of equal wall sides and the length of one side. The apothem is the horizontal common-rafter run; the center-to-corner radius is the hip plan run. Roof pitch converts those plan runs into true centerline lengths.

Worked example: an eight-sided gazebo with 2000 mm wall sides and a 6-in-12 pitch has a 2414.2 mm wall apothem and about 1207.1 mm of rise before the overhang is applied.

The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.

Number of sides

8

Wall side length

2000 mm

Pitch rise

6

Pitch run

12

Horizontal overhang

300 mm

Primary result: Hip rafter centerline: 2878.5 mm.

• Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
• Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
• When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.

This assumes a regular polygon with a central apex and one common pitch. It does not size structural members or deduct ridge blocks, seats, tails, fascia, birdsmouths or member thickness. Check the actual wall polygon corner-to-corner before cutting rafters.