Roof pitch describes how steep a roof is, but there are three different ways to express it: as a ratio (like 6:12), in degrees, or as a slope percentage. Depending on who you are talking to — a framing contractor, a structural engineer, or a building inspector — you may need one format or another. This page provides a complete conversion chart and explains when each notation is appropriate.
Understanding Rise-Over-Run Notation
In the United States and Canada, pitch is most commonly expressed as a ratio of vertical rise to horizontal run, with the run fixed at 12 inches. A 6:12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance. The first number (rise) changes; the second number (run) stays at 12.
This notation is intuitive for carpenters because it directly relates to measurements they can mark on a framing square. When you hear someone say “it’s a four-twelve,” they mean 4 inches of rise per 12 inches of run.
Three Ways to Express Pitch
Ratio (X:12)
Used almost universally among roofing contractors and framers in North America. Appears on architectural plans, shingle manufacturer specs, and building permit applications. Quick to visualize and measure with a speed square or framing square.
Degrees
The angle measured from the horizontal plane. Structural engineers, architects working with international standards, and some building codes reference pitch in degrees. This is also the format used in most mathematical calculations and CAD software.
Slope Percentage (%)
Calculated as (rise / run) x 100. A 6:12 pitch equals 50% slope. This format appears in civil engineering, road grading, and some European building codes. It is less common in residential roofing conversations in the US but useful when comparing roof slope to drainage or site grading requirements.
Complete Conversion Table: 1:12 Through 24:12
The degree value is calculated as arctan(rise / 12). The slope percentage is (rise / 12) x 100. The pitch factor (also called the roof slope multiplier) represents how much larger the actual roof surface is compared to the flat footprint area.
| Pitch | Degrees | Slope % | Pitch Factor |
|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.003 |
| 2:12 | 9.46° | 16.7% | 1.014 |
| 3:12 | 14.04° | 25.0% | 1.031 |
| 4:12 | 18.43° | 33.3% | 1.054 |
| 5:12 | 22.62° | 41.7% | 1.083 |
| 6:12 | 26.57° | 50.0% | 1.118 |
| 7:12 | 30.26° | 58.3% | 1.157 |
| 8:12 | 33.69° | 66.7% | 1.202 |
| 9:12 | 36.87° | 75.0% | 1.250 |
| 10:12 | 39.81° | 83.3% | 1.302 |
| 11:12 | 42.51° | 91.7% | 1.357 |
| 12:12 | 45.00° | 100.0% | 1.414 |
| 13:12 | 47.29° | 108.3% | 1.474 |
| 14:12 | 49.40° | 116.7% | 1.537 |
| 15:12 | 51.34° | 125.0% | 1.601 |
| 16:12 | 53.13° | 133.3% | 1.667 |
| 17:12 | 54.78° | 141.7% | 1.734 |
| 18:12 | 56.31° | 150.0% | 1.803 |
| 19:12 | 57.72° | 158.3% | 1.873 |
| 20:12 | 59.04° | 166.7% | 1.944 |
| 21:12 | 60.26° | 175.0% | 2.016 |
| 22:12 | 61.39° | 183.3% | 2.088 |
| 23:12 | 62.45° | 191.7% | 2.162 |
| 24:12 | 63.43° | 200.0% | 2.236 |
How the Math Works
The conversion from ratio to degrees uses the arctangent function:
Degrees = arctan(rise / run) = arctan(rise / 12)
For slope percentage, the calculation is straightforward:
Slope % = (rise / 12) × 100
The pitch factor (roof slope multiplier) uses the Pythagorean theorem:
Pitch Factor = √(rise² + 12²) / 12
This multiplier is important for material estimation. If your flat footprint is 1,500 square feet and the pitch factor is 1.202 (for an 8:12 pitch), the true roof surface area is 1,500 × 1.202 = 1,803 square feet. You can calculate this automatically with the roof pitch calculator.
When Each Format Is Used
Contractors and Framers: Ratio
In nearly all residential construction in the US, roofers and framers communicate pitch as X:12. Architectural plans mark pitch with a small triangle symbol showing rise over run. Speed squares are calibrated in this format. If you are getting quotes from roofing contractors, this is the notation they will use and expect.
Engineers and Architects: Degrees
Structural calculations, load analysis, and international building standards often work in degrees. If a wind load calculation requires the roof angle, or if you are working with software that asks for angle input, convert the ratio to degrees using the table above.
Building Codes: Both
Building codes may reference minimum slope requirements using either format. For example, a code might require “a minimum slope of 2:12” for asphalt shingles, or specify “at least 14 degrees” for a fire setback calculation. Always check your local code language to know which format applies to your situation.
Visual Explanation: Rise Over Run
Imagine a right triangle drawn on the side of your roof. The horizontal leg (base) is the run — always 12 inches in standard notation. The vertical leg (height) is the rise — the number that changes. The hypotenuse is the actual roof surface along the slope.
A 4:12 pitch forms a relatively shallow triangle (18.43 degrees) — common for low-slope residential roofs and covered porches. A 12:12 pitch forms a perfect 45-degree triangle — a steep roof often seen in A-frame cabins or Gothic revival architecture.
Most residential roofs in the US fall between 4:12 and 9:12. Anything below 2:12 is considered low-slope (often requiring membrane or built-up roofing rather than shingles). Anything above 12:12 is uncommon outside of decorative turrets or steeply pitched dormers.
Using the Pitch Factor for Estimates
The pitch factor column is particularly useful when estimating materials. If you know the building footprint from aerial imagery or a floor plan, multiply by the pitch factor to get true roof surface area. This number feeds directly into roof area calculations and material estimates.
For a more detailed guide on taking measurements, see how to measure roof pitch.
Sources and Notes
Degree and percentage values are derived from standard trigonometric formulas (arctangent). Pitch factor values are calculated as the hypotenuse length of a right triangle with a run of 12, divided by 12. These are mathematical constants and do not vary by source. Common pitch ranges for residential construction are based on general US building practice and may differ in other countries.