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Gambrel Roof Geometry Calculator

This Gambrel Roof confines to a semicircle, and starts as the top half of an equal sided octagon. Move slider or directly enter angle to alter sweep angle of lower rafters and change the shape.
Check Overhang to calculate rafter overhang equal to the lower level cut at the full rafter depth. With overhang selected, move the slider to increment - decrement the birdsmouth seat width to suit. Geometric calculator only Geometric calculator only. Check local building regulations for sizes, spans angles etc.

Wall Width
Sweep Angle
Rafter Depth
Ridge Thick
Purlin Thick
If using gussets to connect rafters, check the Gussets box and enter Gusset Base width to create gusset dimension diagrams. (see diagrams)

Direct Measure Left click, release and drag in main diagram to directly measure dimensions at scale.

Email this Calculation Creates a link to save or Email current calculation


Sweep Angle








Need these calculations on-site? Try the site with an iPad or Android Tablet. With a tablet, you can directly measure angles for input to the Roofing and Pitch Angle calculator apps. Lay the tablet on an incline and tap to measure angle. Tap again to capture angle and auto calculate roof, pitch, angles etc. The buttons appear automatically when you visit with a device capable of pitch measurement.






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Create PDF files to print diagrams on current page. Print large images over multiple pages Printing to Scale Help and Plan Printing.

Slider Controls To fine tune Slider Controls click to select and use (cursor) keyboard keys.

Use your iPad or Android Tablet On-Site Your iPhone or Android is a valuable On-Site tool!
Lay your device on an angled surface (roof ?) to directly measure angles and automatically calculate Roofing and Pitch Angle Apps.

If you've benefited from this free service please consider a small donation to:
Blue Dragon Children's Foundation



Contact Us
ph: (Australia) +61 7 40987645 mob: 0438 165 753

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Questions or Suggestions? ph: +61 7 40987645

ALWAYS CHECK WITH YOUR LOCAL BUILDING AUTHORITY BEFORE LAYING OUT OR BUILDING ANYTHING
AND FOLLOW ALL LOCAL CODES. VERIFY ALL DIMENSIONS AND ANGLES BEFORE CONSTRUCTION.
All calculators on this site are GEOMETRIC only. Check local regulations for sizes, spacings and all engineering requirements.


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