Pitch & Span

Roof Pitch Calculator

This calculator converts roof pitch between three notations — x/12 (rise per 12" of run), degrees from horizontal, and percent slope — using angle = arctan(pitch ÷ 12). Enter any one value and get the other two instantly, with a live triangle diagram.

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      Roof Pitch Calculator

      This calculator converts roof pitch between three notations — x/12 (rise per 12" of run), degrees from horizontal, and percent slope — using angle = arctan(pitch ÷ 12). Enter any one value and get the other two instantly, with a live triangle diagram.

      Scenario presets

      Rise in inches per 12" of run — read off a speed square or rafter square.

      Roof rafter profile diagram Live-updating roof profile showing run, rise, rafter length, and cut angles.
      Angle (degrees) 26.6°
      Pitch (x/12)
      6/12
      Slope (percent)
      50%
      Slope factor
      1.118

      Worked example

      A framer measures a roof with a speed square and reads 7/12. The permit drawings need the angle in degrees.

      Angle. angle = arctan(pitch ÷ 12) = arctan(7 ÷ 12) = arctan(0.5833) = 30.26°.

      Percent slope. percent = (pitch ÷ 12) × 100 = (7 ÷ 12) × 100 = 58.3%.

      Slope factor. √(144 + 7²) ÷ 12 = √193 ÷ 12 = 1.1577 — every 12" of horizontal run needs 1.1577 × 12" = 13.89" of actual roofing material along the slope.

      How it works

      Every roof pitch describes the same right triangle: a 12" horizontal run, a vertical rise equal to the pitch number, and a sloped hypotenuse. All three notations below describe that one triangle.

      angle = arctan(pitch ÷ 12) · percent = (pitch ÷ 12) × 100

      • x/12 pitch — the framing trade's default. Read directly off a speed square; used for rafter and truss cut angles.
      • Degrees — used on permit drawings, engineering documents, and digital angle finders.
      • Percent slope — common on drainage and low-slope commercial roofing specs, and on some European plans.
      • Slope factor — the multiplier that turns a flat, horizontal measurement into a true, sloped one. Every material calculator on this site (rafter, shingle, metal, area) uses it.

      Pitch correction factor table (1/12 – 24/12)

      The full range of standard roof pitches, their angle from horizontal, and the slope factor (multiplier applied to a flat-plan measurement to get the true, sloped length).

      Pitch Angle Slope factor OSHA classification
      1/12 4.8° 1.0035 Low-slope
      2/12 9.5° 1.0138 Low-slope
      3/12 14° 1.0308 Low-slope
      4/12 18.4° 1.0541 Low-slope
      5/12 22.6° 1.0833 Steep-slope
      6/12 26.6° 1.118 Steep-slope
      7/12 30.3° 1.1577 Steep-slope
      8/12 33.7° 1.2019 Steep-slope
      9/12 36.9° 1.25 Steep-slope
      10/12 39.8° 1.3017 Steep-slope
      11/12 42.5° 1.3566 Steep-slope
      12/12 45° 1.4142 Steep-slope
      13/12 47.3° 1.4743 Steep-slope
      14/12 49.4° 1.5366 Steep-slope
      15/12 51.3° 1.6008 Steep-slope
      16/12 53.1° 1.6667 Steep-slope
      17/12 54.8° 1.7341 Steep-slope
      18/12 56.3° 1.8028 Steep-slope
      19/12 57.7° 1.8727 Steep-slope
      20/12 59° 1.9437 Steep-slope
      21/12 60.3° 2.0156 Steep-slope
      22/12 61.4° 2.0883 Steep-slope
      23/12 62.4° 2.1619 Steep-slope
      24/12 63.4° 2.2361 Steep-slope

      OSHA classification per 29 CFR 1926.500(b): a "low-slope roof" is one with a slope of 4-in-12 or less, which changes the fall-protection requirements that apply to roofing work — see your competent person or OSHA's fall-protection standard for what's required on your job.

      Tips from the field

      • Measure pitch at the roof itself, not from a photo or a satellite image — foreshortening makes low-slope roofs look steeper than they are.
      • When converting for a permit set, round degrees to one decimal place; inspectors expect a specific number, not a long decimal.
      • If a spec sheet gives you a minimum slope in percent (common for low-slope membrane roofing), convert to x/12 before checking it against standard shingle manufacturer minimums.
      • Digital angle finders read from vertical on some models and from horizontal on others — check which before trusting the number.
      • A pitch under about 2/12 usually needs a roofing material rated for low-slope application, not standard shingles.

      What this tool does not do

      • Does not calculate rafter length, run, or rise — use the Rafter Length Calculator for that.
      • Does not calculate roof area or material quantities — use the Roof Square Footage or Roof Area Calculator.
      • Does not tell you which roofing material is rated for a given pitch — check the manufacturer's specification sheet.

      For the same conversion with more emphasis on the material-quantity multiplier, see the Roof Slope Calculator. For rafter geometry built on this same pitch, see the Rafter Length Calculator.

      Did this calculator help you?

      Frequently asked questions

      These are the questions that come up when a pitch number needs to become an angle, or an angle needs to become a pitch, for a cut list or a permit drawing.

      What does "roof pitch" actually measure?

      Roof pitch is the ratio of vertical rise to horizontal run, expressed as rise per 12 inches of run — "6/12" means the roof climbs 6 inches for every 12 inches it runs horizontally. It is a ratio, not an angle, though the two convert directly.

      How do I read pitch off a speed square?

      Hook the square's pivot point on the top edge of the rafter, then rotate it until the "common" scale lines up with the edge — the number it lands on is the pitch. This is the fastest field method and needs no math.

      Why do roofers use x/12 instead of degrees?

      Framing squares and speed squares are graduated in twelfths, so x/12 maps directly onto a physical tool. Degrees require a protractor or digital angle finder, which most framers don't carry on their belt.

      What is a "low-slope" roof and why does it matter?

      Roofs under about 2/12 to 3/12 are considered low-slope and typically need different roofing materials (membrane or modified bitumen) instead of standard asphalt shingles, which are rated for a minimum slope by the manufacturer.

      What is the steepest common residential roof pitch?

      Most residential roofs run 4/12 to 9/12. Pitches above 12/12 (45°) are considered steep-slope and usually need fall-protection gear and specialized fastening — they show up on A-frame cabins and some Victorian-style homes.

      Does a steeper pitch always mean a more expensive roof?

      Usually, yes — steeper pitches need more material (see the slope factor in the reference table), take longer to work safely, and often require additional fall protection. The Roof Replacement Cost Calculator factors complexity into its range.

      Can I convert a percent slope (like on a drainage spec) to a roof pitch?

      Yes. Percent slope is rise over run times 100, so 50% slope equals 6/12 pitch. Switch this calculator to Percent mode and enter the value directly.

      Why do two roofs with the same pitch look different in photos?

      Roof pitch is a ratio, so the visual steepness also depends on the building's width. A 6/12 pitch on a 40 ft span rises much higher at the ridge than the same 6/12 pitch on a 20 ft span.

      Is pitch measured the same way for hip and gable roofs?

      Yes — pitch is a property of each roof plane's slope, not the roof's overall shape. A hip roof and a gable roof can both be built at 6/12; the difference is in how the planes intersect, not the pitch itself.

      How accurate does my pitch measurement need to be?

      For material estimating, rounding to the nearest half-pitch (e.g., 6/12 vs 6.5/12) is usually fine. For rafter cuts and framing angles, use the actual measured pitch — small errors compound over a long rafter run.

      What is the relationship between pitch and the roof angle in degrees?

      angle = arctan(pitch ÷ 12). A 6/12 pitch is arctan(0.5) ≈ 26.57°. This calculator does that conversion instantly in either direction.

      Does pitch affect how much attic space I have?

      Yes — for a given building width, a steeper pitch creates more vertical headroom under the ridge, which is why steep-pitch homes often have usable attic or loft space where a low-slope roof would not.

      Why does the correction factor table stop at 24/12?

      24/12 is a 63.4° angle — beyond that, a roof plane is closer to a wall than a roof, and standard roofing material and framing methods no longer apply cleanly. It is a practical, not a mathematical, limit.

      How we checked this page

      Written by
      Pitch & Span Editorial
      Reviewed by
      Conversion formulas checked against standard trigonometric identities and cross-checked against a physical speed square at 4/12, 6/12, and 12/12.
      Last reviewed
      2026-07-28
      Publisher
      Pitch & Span
      Scope
      Roof pitch, angle, and slope notation conversion
      What we checked
      • 12/12 pitch confirmed to equal exactly 45° and 100% slope.
      • Round-trip conversion (pitch → degrees → pitch) checked to return the original value at full precision.
      • Slope factor cross-checked against the Rafter Length Calculator's geometry for consistency across the site.

      Methodology

      Cite this calculator

      Pitch & Span. "Roof Pitch Calculator." Pitch & Span, https://pitchandspan.com/roof-pitch-calculator/. Accessed .

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