Roof Pitch Calculator
Calculate roof pitch from rise and run, convert to degrees and slope percentage, and estimate rafter length, ridge height, and roof area for planning purposes.
Calculate roof pitch from rise and run, convert to degrees and slope percentage, and estimate rafter length, ridge height, and roof area for planning purposes.
Roof pitch is the ratio of vertical rise to horizontal run. Standard notation is "X:12" (rise per 12" of run).
Roof pitch is how steep your roof is. Expressed as a ratio like "X:12" — meaning X inches of rise for every 12 inches of run. A 6:12 pitch rises 6 inches over 12 inches horizontal. Pitch affects materials, labor, installation speed, and roof lifespan. Steep pitches shed water fast but cost more and need careful work. Shallow pitches are faster to install but demand better drainage systems. A 4/12 pitch is about the flattest you'll see with asphalt shingles. Anything under that needs a membrane — rolled roofing or TPO.
No climbing required. Use a smartphone level app that shows pitch, or grab a 12-inch level and measure tape. Hold the level against the roof face, read the angle, convert using tables. Works if you've got a clear roof line at eye level.
Binoculars work too. If you know the height and width, you can triangulate. Less precise, but gets you in the ballpark without getting on a ladder.
Attic method is most accurate if you can safely access it. Measure 12 inches horizontally from a rafter toward the peak, then measure vertical rise at that mark. That vertical number in inches is your pitch. Example: 6 inches rise over 12 inches run = 6:12 pitch.
Bring a level, tape, and straight edge. Mark your horizontal run with pencil. Take vertical measurement. Check multiple rafters — old buildings sometimes have different pitch on different sections. Double-check before you order materials.
Pitch is a ratio (6:12). Slope is degrees (26.57°). Same thing, different language. Pitch is common in roofing, slope in construction docs. Both tell you how steep your roof is — just different units.
Below 4:12 is low-slope territory — needs special materials and techniques. Above 12:12 is rare in residential work because structure and install complexity explode.
Know your pitch? Calculate actual roof area. Ground-level footprint is always smaller than actual roof area because of slope. Multiply footprint by pitch multiplier:
Actual Roof Area = Footprint Area × Pitch Multiplier
Example: 32-foot-wide by 50-foot-long building with 6:12 pitch has 1,600 sq ft footprint. Multiplier for 6:12 is 1.1180. Actual area: 1,600 × 1.1180 = 1,788.8 sq ft. You order materials based on actual area, not footprint. Miss this and you'll underestimate.
Low-slope (below 4:12): Needs materials designed for gentle slopes. Built-up tar and gravel, TPO, EPDM rubber, modified bitumen, metal with standing seams. These are membranes or fluid-applied — they create waterproof barriers without relying on overlap like shingles do.
Steep-slope (4:12+): Can use traditional shingles because pitch naturally sheds water. Asphalt shingles, wood shakes, slate, tile, metal seam — all work. Steeper = better drainage = longer roof life. Steeper roofs generally age better.
Pitch determines material choice. Asphalt shingles on a 2:12? They fail from water intrusion. 12:12 on a rubber membrane? Overkill and expensive. Get pitch right and specify correct materials first time.
Steeper = more material. A 12:12 pitch uses about 20% more shingles than a 6:12 over the same footprint. Shingles, underlayment, flashing, ridge cap, trim — all go up. Labor costs jump too — safety requirements, slower install, complex cuts. Safety gear becomes mandatory on steeper pitches.
Always estimate based on actual roof area, not footprint. Plan for waste: 10% for simple rectangular roofs, 20% for complex roofs with valleys, dormers, and multiple pitches. Waste happens, budget for it.
| Pitch | Angle (°) | Slope % | Multiplier | Common Uses |
|---|---|---|---|---|
| 1:12 | 4.8° | 8.3% | 1.0035 | Low-slope, metal roofing |
| 2:12 | 9.5° | 16.7% | 1.0138 | Low-slope, TPO, EPDM |
| 3:12 | 14.0° | 25.0% | 1.0308 | Low-slope, standing seam |
| 4:12 | 18.4° | 33.3% | 1.0541 | Residential standard, shingles |
| 5:12 | 22.6° | 41.7% | 1.0833 | Residential, excellent drainage |
| 6:12 | 26.6° | 50.0% | 1.1180 | Very common residential |
| 7:12 | 30.3° | 58.3% | 1.1577 | Steeper residential |
| 8:12 | 33.7° | 66.7% | 1.2019 | Steep residential |
| 9:12 | 36.9° | 75.0% | 1.2500 | Very steep, traditional |
| 10:12 | 39.8° | 83.3% | 1.3015 | Steep, high-end residential |
| 11:12 | 42.5° | 91.7% | 1.3563 | Very steep, specialized |
| 12:12 | 45.0° | 100.0% | 1.4142 | 45° pitch, dramatic |
Smartphone level app that shows angle — easiest. Or 12-inch level and tape measure held against a visible roof edge. Read the angle, convert using tables. If you can see the peak from a distance, use binoculars and estimate rise over run. Attic is most accurate if you can safely get in — measure 12" horizontal, measure vertical rise at that mark. That's your pitch number.
4:12 is 18.4 degrees. Formula: angle = arctan(rise/12). So arctan(4/12) = arctan(0.3333) = 18.4°. This is the industry minimum for asphalt shingles — steep enough to shed water effectively, but still manageable to work on.
4:12 minimum. Some manufacturers allow 3:12 with extra underlayment, but 4:12 is the standard. Below 4:12 and you'll get water intrusion, shortened lifespan, warranty issues. For below 4:12, use TPO, EPDM, or modified bitumen instead. Don't guess here — right material matters.
Below 6:12: roofers can work safely with fall protection. 6:12 to 8:12: fall protection is critical. Above 8:12: steep territory — specialized equipment, harnesses, staging required. Homeowners? Don't walk steeper than 6:12 without pro equipment. Below 4:12 is relatively accessible for maintenance if weather's good and surface has friction.
Steeper costs 20-50% more. A 12:12 might run 40% higher than 4:12 over same footprint. Why? (1) More actual roof area because of slope, (2) labor takes longer and costs more, (3) special equipment and safety staging. Labor rates jump with pitch. Steeper means slower, safer installation. Waste is higher on steep pitches too.
