Roof Pitch Calculator with Framing Diagram
A free printable roof pitch calculator. Enter the span and set the pitch as an angle, an X:12 ratio or a rise, and get the rise, run, rafter length, ridge height and slope — with a clearly labelled gable-roof framing cross-section showing the rafters, ridge board, ceiling joist / tie, king post and wall plates, every dimension marked. Print it or save it as a PDF.
Setting out a roof starts with one relationship: the pitch. The pitch ties together the span (the width the roof crosses), the run (half the span, from the wall to the ridge), the rise (how high the ridge sits above the wall plate) and the rafter length (the sloping timber that runs from plate to ridge). Fix any of these and the geometry follows. This calculator lets you set the pitch whichever way suits you — as an angle in degrees, as a rise-to-run ratio, in the builder's X-in-12 style, or by entering the rise directly — and instantly works out all the others.
Enter the span and choose a pitch, and the sheet returns the run, the rise, the pitch angle in degrees, the equivalent X-in-12 and rise:1 ratios, and the rafter length — both the plate-to-ridge length and the full length including the eaves overhang you specify. These are the numbers you need to order timber and set out cuts, worked from the standard right-angle-triangle relationships of a symmetric gable roof.
The heart of the sheet is a labelled cross-section of the roof drawn to your figures. It shows the two rafters meeting at a ridge board, the ceiling joist or tie beam across the bottom, a king post rising from the tie to the ridge, and the wall plates on top of the walls, with the pitch angle arc, the span, run, rise and rafter length all dimensioned. It makes a clear one-page reference to take to the workshop or the site, or to check a design before you cut a single length of timber.
Printing at exact scale
Every sheet is drawn in real millimetres and prints at exact physical scale. For accurate output, set Scale = 100% (Actual size) and Margins = None in your browser's print dialog. Not sure your printer is honest? Run the printer ruler test first to confirm 50 mm really measures 50 mm. Prefer a file? Use the PDF, PNG or SVG buttons to download the sheet instead of printing — PDF and SVG keep the exact dimensions, and PNG is a 300 DPI image.
Frequently asked questions
What is roof pitch?
Roof pitch is the steepness of the roof — how much it rises for a given horizontal distance. It can be expressed as an angle in degrees, as a ratio of rise to run, or in the X-in-12 style used by many builders (the rise in inches for every 12 inches of run).
How do I calculate rafter length?
For a symmetric gable roof the rafter is the hypotenuse of a right-angled triangle whose base is the run (half the span) and whose height is the rise. So rafter = √(run² + rise²). The calculator does this for you and adds the sloping length of any eaves overhang.
What's the difference between span and run?
The span is the full width the roof crosses, wall to wall. The run is half of that — the horizontal distance from one wall to the ridge in the centre. Rise is measured over the run, not the span.
How do I convert between degrees and X-in-12?
They describe the same angle. X-in-12 means the roof rises X units for every 12 across, so the angle is arctan(X ÷ 12). The calculator shows the pitch as degrees, as X-in-12 and as a rise:1 ratio at the same time, so you can switch between them.
What roof members does the diagram show?
The cross-section labels the rafters (the sloping timbers), the ridge board at the apex, the ceiling joist or tie beam across the bottom, the king post rising from the tie to the ridge, and the wall plates the rafters sit on. It also marks the eaves overhang.
Does it allow for the eaves overhang?
Yes — enter the horizontal overhang each side and the sheet adds its sloping length to the rafter, so the rafter figure is the full length you need to cut including the eaves projection.
Is the geometry exact?
The trigonometry is exact for a symmetric gable measured to the member centre-lines. It doesn't automatically deduct for rafter depth, the birdsmouth seat cut, ridge-board thickness or plumb cuts — allow for those when marking out and cutting the actual timber.
Is it really free?
Yes. Every template on printsheet.io is completely free, with no sign-up, no account and no watermark. Generate as many sheets as you like.
How do I get an exact-scale print?
Choose your paper size, then in the print dialog set Scale to 100% or “Actual size” and Margins to None. The sheet is defined in real millimetres, so it prints at true size. Use the calibration ruler page to verify.
Which paper sizes are supported?
A4, A5, A3, A6, US Letter, Legal and Tabloid, in portrait or landscape. Pick the size that matches the paper loaded in your printer.
Can I save it as a PDF instead of printing?
Yes — choose “Save as PDF” as the printer in your browser's print dialog. The PDF keeps the exact millimetre dimensions.
Can I download it as an image (PNG or SVG)?
Yes — as well as Print and PDF, every sheet has a PNG and an SVG download button. PNG gives you a high-resolution (300 DPI) image at the exact page size, ideal for pasting into a document or sharing. SVG is a scalable vector file that stays razor-sharp at any size and can be edited in tools like Inkscape or Illustrator. Both are generated in your browser from the sheet you see on screen.