Roof Pitch Chart
Three numbers describe the same slope and every trade uses a different one: builders say 6/12, surveyors say 26.6 degrees, civil drawings say 50 percent. The fourth column is the one that costs money — the multiplier that turns a floor plan into actual roof area.
Generated from the same data the calculators use — a chart and a calculator on this site cannot disagree.
Pitch conversion and area multiplier
| Pitch | Degrees | Percent | Area multiplier | Roofing permitted |
|---|---|---|---|---|
| 1/12 | 4.8° | 8.3% | ×1.0035 | Shingles not permitted |
| 2/12 | 9.5° | 16.7% | ×1.0138 | Shingles, double underlayment |
| 2.5/12 | 11.8° | 20.8% | ×1.0215 | Shingles, double underlayment |
| 3/12 | 14.0° | 25.0% | ×1.0308 | Shingles, double underlayment |
| 4/12 | 18.4° | 33.3% | ×1.0541 | Standard shingle install |
| 5/12 | 22.6° | 41.7% | ×1.0833 | Standard shingle install |
| 6/12 | 26.6° | 50.0% | ×1.1180 | Standard shingle install |
| 7/12 | 30.3° | 58.3% | ×1.1577 | Standard shingle install |
| 8/12 | 33.7° | 66.7% | ×1.2019 | Standard shingle install |
| 9/12 | 36.9° | 75.0% | ×1.2500 | Standard shingle install |
| 10/12 | 39.8° | 83.3% | ×1.3017 | Standard shingle install |
| 12/12 | 45.0° | 100.0% | ×1.4142 | Standard shingle install |
| 14/12 | 49.4° | 116.7% | ×1.5366 | Standard shingle install |
| 16/12 | 53.1° | 133.3% | ×1.6667 | Standard shingle install |
| 18/12 | 56.3° | 150.0% | ×1.8028 | Standard shingle install |
| 24/12 | 63.4° | 200.0% | ×2.2361 | Standard shingle install |
How to read this chart
Below 2:12 asphalt shingles cannot shed water reliably and are not permitted. That is low-slope roofing and needs a membrane system, standing seam or rolled roofing instead.
Between 2:12 and 4:12, IRC R905.2 and every shingle manufacturer require two layers of underlayment. Installing a single layer on a 3:12 roof voids the warranty and is a common source of claims.
Multiply the building footprint by the area multiplier to get real roof surface. A 6:12 roof is 12 percent larger than the ground it covers; a 12:12 roof is 41 percent larger. Ordering shingles off the floor plan is how jobs come up short.
Roofs up to about 6:12 are generally walkable with proper footwear. Above that, roof jacks, staging or fall arrest become necessary.
Sources
- Right-triangle trigonometry
- IRC R905.2 — asphalt shingle slope requirements
Reference values. Manufacturer instructions govern any specific product and may be stricter than code. Confirm low-slope assemblies with your building department.
Frequently asked questions
What does 6/12 pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. It is a ratio, so a 6/12 roof on a wider building is taller but the pitch is unchanged.
How do I measure pitch on an existing roof?
Hold a level horizontally against a rafter, mark 12 inches along it, and measure straight down to the roof surface. That vertical distance is the rise per foot.
What is the minimum pitch for shingles?
Two in twelve, and only with two layers of underlayment. Below that the water moves too slowly and wind can drive it back under the courses.
Why is the area multiplier important?
Because roofing is sold by sloped area, not footprint. It converts a floor plan directly into shingle, underlayment and sheathing quantities.