Free Roof Pitch Calculator
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Roof Pitch Calculator

Enter rise and run to calculate pitch angle, ratio, and rafter length. The diagram updates live as you type.

Measurements

Rafter Length Calculator
Full width — run is half the span for a symmetric roof

Results

Rise Run
Pitch Ratio 6 / 12
Angle 26.57°
Slope (%) 50.0%
Rafter per ft of run 13.42 in

Material Compatibility

Common Roof Pitches Reference

PitchDegreesTypical Use
1/12 4.8° Nearly flat — membrane roofing only
2/12 9.5° Low slope — minimum for shingles with underlayment
3/12 14.0° Low slope — standard shingles with ice/water shield
4/12 18.4° Moderate — most common residential pitch
5/12 22.6° Moderate — good rain/snow shedding
6/12 26.6° Standard — popular in northern climates
8/12 33.7° Steep — all materials, excellent shedding
10/12 39.8° Steep — dramatic look, walk boards needed
12/12 45.0° Very steep — 45° angle, specialty installation

How Roof Pitch Is Calculated

Roof pitch describes the steepness of a roof as the ratio of vertical rise to horizontal run. The standard convention uses 12 as the run base — so a "6/12 pitch" means 6 inches of rise for every 12 inches of horizontal run.

From Rise and Run to Degrees

The angle in degrees is calculated using the arctangent function: angle = arctan(rise ÷ run). For a 6/12 pitch: arctan(6/12) = arctan(0.5) ≈ 26.57°.

Rafter Length Formula

Rafter length follows the Pythagorean theorem: rafter = √(rise² + run²). For practical use, the "rafter factor" per foot of run is √(1 + (pitch/12)²) × 12 inches. Multiply this by total run length and add overhang for the cut length.

Slope Percentage

Slope percentage is simply (rise ÷ run) × 100. A 6/12 pitch = 50% slope. This notation is common in civil engineering and road grading but less common in residential roofing.

Choosing the Right Pitch

Pitch affects material options, construction cost, attic space, and weather performance. Steeper roofs shed water and snow faster but cost more due to increased material area and safety requirements. Lower pitches are economical but limit material choices and may need enhanced waterproofing.

Low Pitch (0/12 – 3/12)

Flat to shallow roofs. Require membrane roofing (TPO, EPDM, built-up) or special low-slope shingles with full ice-and-water shield underlayment. Common on commercial buildings and modern residential designs.

Moderate Pitch (4/12 – 6/12)

The most common residential range. Supports asphalt shingles, metal panels, clay tiles, and most other materials. Provides a good balance of cost, aesthetics, and weather performance.

Steep Pitch (7/12 – 12/12+)

Dramatic appearance with excellent water and snow shedding. Requires walk boards or scaffolding for installation. Increases material and labor costs but maximizes attic space. Slate, cedar shakes, and architectural shingles look best at steep pitches.

Frequently Asked Questions

What is roof pitch?

Roof pitch is the steepness or slope of a roof, expressed as a ratio of vertical rise to horizontal run. For example, a 4/12 pitch means the roof rises 4 inches for every 12 inches of horizontal distance. It can also be expressed as an angle in degrees — a 4/12 pitch equals approximately 18.4°.

How do I measure roof pitch from the ground?

From ground level, hold a speed square or pitch gauge against a rafter tail or fascia board. Alternatively, measure from inside the attic: place a level horizontally against a rafter, mark 12 inches along the level, then measure the vertical distance from that mark straight up to the rafter. That vertical measurement is your rise per 12 inches of run.

What roof pitch is best for my climate?

In areas with heavy snow or rain, steeper pitches (6/12 to 12/12) shed water and snow more effectively. In hot, dry climates, lower pitches (2/12 to 4/12) are common and more economical. Hurricane-prone areas often use hip roofs at 4/12 to 6/12 for wind resistance. Local building codes may mandate minimum pitches.

What is the minimum roof pitch for shingles?

Most asphalt shingle manufacturers require a minimum 2/12 pitch (about 9.5°). Some low-slope shingles are rated for 2/12, but standard 3-tab and architectural shingles typically require at least 4/12. Below 2/12, you'll need a continuous membrane system like TPO, EPDM, or built-up roofing.

How do I calculate rafter length from pitch?

Rafter length equals the square root of (rise² + run²). For example, with a 6/12 pitch and a 12-foot run: rise = 6 feet, so rafter length = √(6² + 12²) = √(36 + 144) = √180 ≈ 13.42 feet. Add overhang length for the total rafter. This calculator computes this automatically from your inputs.