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Roof Pitch Calculator

Convert between roof pitch, angle, and rafter length — rise/run or degrees, metric or imperial.

  • roof
  • pitch
  • slope
  • angle
  • rafter
  • rise
  • run
  • degrees
  • gradient

About Roof Pitch Calculator

Roof pitch is described three different ways depending on who's talking: a fraction like 6/12 on a North American framing plan, a ratio like 1:2 in metric drawings, and an angle in degrees on a digital level. They're all the same slope, and this calculator moves freely between them — enter a rise and run and it gives you the angle and both pitch notations, or type an angle and it works backwards to the ratio.

It also returns the rafter factor, the single most useful number for framing: the slope length per unit of horizontal run. Multiply it by your run and you have the rafter length. Finally it categorises the pitch as low, conventional, or steep and notes which roofing materials suit it, since a slope that's fine for standing-seam metal may be too shallow for asphalt shingles.

How to use

Choose "Rise & run" to enter the roof's vertical rise and horizontal run, or "Angle" to start from a pitch angle in degrees. Pick metric or imperial — the pitch ratio is the same number either way, but the result leads with the convention your region uses (1:n for metric, X/12 for imperial) and shows the other beneath it.

The headline gives the pitch and angle with a category badge. The rafter card shows the slope factor — the rafter length per metre or foot of run — and, when you've entered an actual run, the total rafter length for it. Add to that figure for the eaves overhang and the ridge connection, which depend on your detail. The materials note flags whether the slope suits shingles, metal, or a low-slope membrane.

Frequently asked questions

  • What does a roof pitch like 6/12 mean?

    It means the roof rises 6 units for every 12 units of horizontal run — a rise-over-run ratio expressed against a fixed run of 12, which is the North American convention. A 6/12 pitch works out to about 26.6°. In metric the same slope is written 1:2 (one up for every two along). This calculator shows whichever notation you prefer and converts to the angle automatically.

  • How do I convert roof pitch to degrees?

    Take the arctangent of the rise divided by the run: angle = atan(rise ÷ run). A 6/12 pitch is atan(6/12) = atan(0.5) ≈ 26.6°, and a 12/12 pitch is atan(1) = 45°. Working the other way, the slope equals the tangent of the angle. The calculator does both directions, so you can start from rise and run or from an angle off a digital level.

  • How do I calculate rafter length from pitch?

    The rafter is the hypotenuse of the rise-and-run triangle, so its length is √(rise² + run²). A handy shortcut is the rafter factor — √(1 + slope²) — which is the rafter length per unit of run; multiply it by your run to get the length. Remember the figure is the line from wall to ridge, so add extra for the eaves overhang and the ridge connection.

  • What is considered a low, medium, or steep roof pitch?

    As a rule of thumb, low slope is below about a 3/12 pitch (under ~14°), conventional or medium runs from there to roughly 9/12 (about 14–37°), and steep is anything above that. The bands matter because they govern which materials are suitable and how the roof sheds water and snow. This calculator labels your pitch and notes typical materials for it.

  • What roofing material suits my roof pitch?

    Low slopes generally need a membrane system (EPDM, TPO, or modified bitumen) or standing-seam metal, because water drains slowly and can back up under shingles. Conventional pitches suit asphalt shingles, metal, and most common materials. Steep roofs shed water and snow well and suit shingles, metal, slate, and tile, but use more material per square of plan area and need fall protection. Always follow the manufacturer's minimum-slope rating.

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