Gambrel Roof Framing Geometry

Gambrel Roof Framing Geometry is the professional tool for calculating every dimension, angle, and cut you need to frame a gambrel (barn-style) roof — right from your iPhone or iPad.

Enter your wall width, rafter depth, roof angles, and overhang, and instantly get precise measurements for lower rafters, upper rafters, birdsmouth cuts, joint geometry, gusset plates, purlin offsets, ridge offsets, and total roof area. Every value updates in real time as you adjust parameters.

INTERACTIVE DIAGRAMS • Full cross-section profile of the complete gambrel roof • Detailed lower rafter diagram with birdsmouth seat, plumb cut, and all angles • Detailed upper rafter diagram with tail cut and joint geometry • Top gusset and mid gusset dimension diagrams • Pinch to zoom and pan on every diagram for close-up detail

COMPLETE RESULTS TABLE All computed values organized in collapsible professional sections: • Overall dimensions — total width, height, peak inner height • Lower and upper rafter — length, rise, run, effective length, pitch ratio • Joint geometry — joint angle, half-joint angle, offset, position • Rafter cuts — plumb cuts, tail cuts with exact measurements • Purlin and ridge offsets — half offset, cos/sin components • Birdsmouth — seat width, height offset, max seat, cut length • Gusset plates — angle, base, slope height, slope length • Roof area — total area calculated from roof length

IMPERIAL & METRIC UNITS Switch instantly between imperial (feet-inches-fractions) and metric (millimeters) input modes. Imperial mode uses traditional picker controls with fractions down to 1/16". Metric mode provides direct text entry for fast input. Results display in your chosen system.

SEMI-CIRCLE MODE Constrain the gambrel profile to fit inside a perfect semicircle with one tap. The calculator automatically derives the upper roof angle and lower rafter length from your lower roof angle.

PDF EXPORT Generate a professional multi-page PDF containing all diagrams and the complete results table. Share via email, AirDrop, save to Files, or print directly — perfect for job sites, permit applications, and client presentations.

DISPLAY OPTIONS • Color fill or outline-only diagrams • Show/hide dimension labels • Add a person silhouette for visual scale reference • Adjustable person height for accurate perspective

BUILT FOR PROFESSIONALS Whether you are a carpenter, timber framer, builder, architect, or serious DIYer, this calculator eliminates manual trigonometry and gives you every measurement needed to lay out and cut gambrel roof trusses with confidence.

All calculations are geometric. Always verify results against local building codes and engineering requirements for your specific project.