Roof Pitch Calculator
Roof pitch, angle, and slope factor.
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Roof pitch describes how steep a roof is, usually as a rise over a 12-inch run. Enter the rise and run and this calculator converts it to degrees, percentage slope, and the slope factor you need to find the true roof surface area from a footprint.
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Roof Pitch — The Quick Answer
Pitch is written as rise:12 — a roof that rises 6 inches over every 12 inches horizontally is a 6:12 pitch, about 26.57°. The angle is arctan(rise ÷ 12).
Shortcut
Angle = arctan(rise ÷ run) | Slope factor = √(rise² + run²) ÷ run
Common roof pitches
| Pitch | Angle | Slope factor | Typical use |
|---|---|---|---|
| 3:12 | 14.0° | 1.031 | Minimum for shingles |
| 4:12 | 18.4° | 1.054 | Low-slope roof |
| 6:12 | 26.6° | 1.118 | Common residential |
| 8:12 | 33.7° | 1.202 | Steeper residential |
| 10:12 | 39.8° | 1.302 | Steep roof |
| 12:12 | 45.0° | 1.414 | Very steep |
The slope factor tells you how much more area a sloped roof has than its flat footprint. Multiply your footprint by it to get the true roof area for ordering shingles or membrane.
How It Works
The Formulas
From rise and run to everything else
Formula
Angle = arctan(rise / run) Slope % = (rise / run) × 100 Slope factor = √(rise² + run²) / run Roof area = footprint × slope factor
Variables
Vertical rise
How far the roof climbs, in inches, over the run. A 6:12 pitch has a rise of 6.
Horizontal run
The horizontal distance, conventionally 12 inches, which is why pitch is written as 'rise over 12'.
Area multiplier
How much bigger the sloped surface is than the footprint. Multiply footprint area by it to get true roof area.
Note: Pitch and slope are often used interchangeably in roofing, though strictly 'pitch' is the ratio and 'slope' is the angle. This calculator gives both.
Worked Example: A 6:12 Roof
Pitch to angle, slope factor, and true area
Note rise over a 12-inch run
6:12 → rise 6, run 12
Angle = arctan(rise ÷ run)
arctan(6 ÷ 12) ≈ 26.57°
Slope factor = √(rise² + run²) ÷ run
√180 ÷ 12 ≈ 1.118
True roof area = footprint × factor
1,200 sq ft × 1.118 ≈ 1,342 sq ft
Reference Guide
| Pitch | Angle | Slope factor | Typical use |
|---|---|---|---|
| 3:12 | 14.0° | 1.031 | Minimum for shingles |
| 4:12 | 18.4° | 1.054 | Low-slope roof |
| 6:12 | 26.6° | 1.118 | Common residential |
| 8:12 | 33.7° | 1.202 | Steeper residential |
| 12:12 | 45.0° | 1.414 | Very steep |
What the Pitch Tells You
Covering, area, and reading the number
Steeper roofs shed water fast and suit shingles, slates, and tiles; low-slope roofs drain slowly and need a continuous membrane. Asphalt shingles typically need at least 2:12, and most makers want 4:12 or steeper for a standard install.
Best for: Choosing a compatible roof covering
The sloped surface is larger than the flat area it covers — the slope factor tells you by how much. A 6:12 roof is about 12% bigger than its footprint, so ordering materials off the footprint leaves you short.
Best for: Estimating materials for a re-roof
Steeper roofs create more attic headroom but catch more wind; low roofs hold snow, adding weight. Steeper roofs are also slower and riskier to work on. Follow local codes and manufacturer minimums for any roofing work.
Best for: Weighing the practical trade-offs
What Is Roof Pitch?
Roof pitch describes how steep a roof is, written as rise over a 12-inch run — a 6:12 roof climbs 6 inches for every 12 inches it runs horizontally. Convert it to degrees with arctan(rise ÷ run), so 6:12 is about 26.6° and 12:12 is exactly 45°. Pitch matters because it decides how quickly a roof sheds water, and therefore what covering it can use: steep roofs take overlapping shingles and tiles, while low-slope roofs need a continuous membrane. It also drives the slope factor — the multiplier that turns a footprint into the true (larger) roof area. This calculator converts between pitch, angle, slope percentage, and roof area.
Key Features
💡 Pro Tips
- →Always order roofing materials off the true roof area (footprint × slope factor), not the footprint — a steep roof can be 20%+ larger.
- →Check your covering's minimum pitch: asphalt shingles generally need 4:12 or steeper for a standard install.
- →A quick way to find pitch on an existing roof is to measure the rise over a 12-inch level held horizontally.
- →Degrees and the x:12 ratio describe the same slope — use whichever your plans or materials specify.
Common Mistakes
Ordering materials off the footprint
The sloped roof surface is larger than its footprint. Ignoring the slope factor leaves you short — a 6:12 roof needs about 12% more material than its footprint suggests.
Ignoring the covering's minimum pitch
Shingles below their minimum slope let water creep under the laps and leak. Low-slope roofs need a membrane system, not overlapping shingles.
Confusing pitch with angle
6:12 is not '6 degrees' — it's about 26.6°. Mixing the ratio and the angle leads to badly wrong cuts and estimates.
Research & Citations
Sources and standards referenced for the factual claims on this page
- [1]
International Code Council (ICC) (2021). International Residential Code (IRC) — roof covering slope requirements. ICC.
Minimum slope requirements for roof coverings.
View source - [2]
Asphalt Roofing Manufacturers Association (ARMA) (2022). Shingle slope and installation guidance. asphaltroofing.org.
Guidance on minimum pitch for asphalt shingles.
View source
This calculator is a reference tool, not a substitute for professional advice. Verify important health, financial, legal, or safety decisions with a suitably qualified professional.
Last updated: October 7, 2026
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Frequently Asked Questions
How do I calculate roof pitch?
Measure the rise over a 12-inch run. If the roof rises 6 inches over 12 horizontal inches, the pitch is 6:12. In degrees, that's arctan(6 ÷ 12) ≈ 26.57°.
What is a 4:12 roof pitch in degrees?
About 18.43°. The angle is arctan(4 ÷ 12) = arctan(0.333) ≈ 18.43°, with a slope factor of about 1.054.
How do I find the roof area from the footprint?
Multiply the footprint area by the slope factor. For a 6:12 roof, the factor is about 1.118, so a 1,200 sq ft footprint has a true roof area of 1,200 × 1.118 ≈ 1,342 sq ft.
What is the minimum roof pitch for shingles?
Asphalt shingles generally need at least a 2:12 pitch, and most manufacturers require 4:12 or steeper for standard installation. Below that, you need a low-slope membrane or underlayment system — always check the manufacturer's requirements.