Practical tools for measured work
Polygon Gazebo Roof & Rafter Calculator
Calculate common and hip centerline rafters, rise, plan angles and roof-face area for regular 3–16-sided roofs.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Measure one outside wall face of a regular polygon.
Centerline lengths run from the wall or fascia polygon to the central apex. Apply the ridge block, seat and tail details from the framing plan before cutting.
How it works
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.
Current-input example
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.
Before using the result
- 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.
Limitations
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.
Frequently asked questions
Does side length include the overhang?
No. Enter the wall side length and the horizontal overhang separately. The tool projects the roof perimeter outward from the wall polygon.
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