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Roof Pitch Calculator

Convert between roof pitch (X/12), angle in degrees, rise, run, slope percent, and rafter length. Built by a builder, for builders.

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Tip

Use the same length unit for rise and run (inches, feet, meters — doesn't matter, just be consistent). The pitch ratio and angle are unit-free.

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Understanding Roof Pitch

Roof pitch describes the steepness of a roof. In residential construction, it's almost always expressed as rise over run with a fixed run of 12 — written as X/12. A 6/12 roof rises 6 inches for every 12 inches you travel horizontally. The same roof can also be described by its angle (about 26.57°) or its slope percent (50%).

The math

A roof slope is just the hypotenuse of a right triangle whose legs are rise (vertical) and run (horizontal). All the conversions follow from basic trigonometry:

angle = arctan(rise / run)

rise = run × tan(angle)

rafter length = √(rise² + run²)

pitch (X/12) = (rise / run) × 12

Complete pitch reference: 2/12 through 12/12

Every standard residential pitch from low-slope (2/12) up to the equal-rise-and-run 12/12. The rafter multiplier column is the conversion factor for rafter length: rafter = run × multiplier. So a 6/12 roof with a 14 ft run needs a rafter of 14 × 1.118 ≈ 15.65 ft (before adding overhang).

Pitch Angle Slope % Rafter multiplier Use case
2/129.46°16.67%1.0138Low slope — modified bitumen, EPDM rubber, standing-seam metal
3/1214.04°25.00%1.0308Low slope — asphalt shingles allowed with double underlayment
4/1218.43°33.33%1.0541Conventional asphalt shingles minimum (most building codes)
5/1222.62°41.67%1.0833Common ranch / suburban — gentle but sheds water well
6/1226.57°50.00%1.1180Most common residential — works with every roofing material
7/1230.26°58.33%1.1577Steeper conventional — common in colder climates
8/1233.69°66.67%1.2019Steeper residential — typically allows usable attic space
9/1236.87°75.00%1.2500Steep — common in snowy regions, dramatic profile
10/1239.81°83.33%1.3017Very steep — premium aesthetics, requires roof jacks for work
11/1242.51°91.67%1.3566Very steep — Victorian / Gothic Revival, traditional steep styles
12/1245.00°100.00%1.414245° pitch — A-frame, alpine cabins, maximum snow shedding

Rafter multiplier = √(rise² + 144) / 12. Slope % = rise / run × 100. Angle = arctan(rise / run). For pitches above 12/12 (e.g. 18/12 mansard ≈ 56.3°, 24/12 ≈ 63.4°), use the calculator above — the same formulas extend without change.

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Frequently Asked Questions

What is roof pitch and how is it expressed?

Roof pitch is the steepness of a roof, expressed as the ratio of vertical rise to horizontal run. In the U.S., it's typically written as "X/12" — meaning X inches of vertical rise for every 12 inches of horizontal run. A 6/12 pitch rises 6 inches per foot of run, which equals about 26.57°.

How do I convert pitch to degrees?

Use the inverse tangent: angle = arctan(rise/run). For example, a 4/12 pitch is arctan(4/12) ≈ 18.43°. Going the other way, rise = run × tan(angle). This calculator does both directions automatically.

What's the most common residential roof pitch?

Most residential roofs in North America fall between 4/12 (18.43°) and 9/12 (36.87°). Steeper pitches (10/12 to 12/12) shed snow better and are common in colder regions. Lower pitches (under 4/12) are considered "low slope" and need different roofing materials.

How do I calculate rafter length from pitch?

Rafter length is the hypotenuse of the rise/run right triangle: rafter = √(rise² + run²). For a 6/12 pitch over a 12-foot run, the rafter would be √(6² + 12²) ≈ 13.42 feet (excluding overhang and ridge thickness).

What is slope percent versus pitch?

Slope percent is rise ÷ run × 100. A 6/12 pitch is a 50% slope. Roofers usually use the X/12 pitch notation; engineers and surveyors more often use percent or degrees. All three describe the same thing — just in different units.

Why do roofs use a /12 ratio instead of just degrees?

Tradition and convenience. A framing square has 12-inch markings, so measuring rise per 12 inches of run is the fastest way to mark cuts on rafters in the field. The X/12 system became standard in U.S. residential framing for that reason.

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