Roof pitch calculator
Rise and horizontal run: you get roof pitch in percent, degrees and x/12, plus the pitch factor.
Slope
50 %
- Slope50 %
- Angle26.57 °
- Pitch (x in 12)6 /12
- Pitch factor1.12
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How it's calculated (visible formula)
% = rise ÷ run × 100; angle = arctan(rise ÷ run); pitch = rise ÷ run × 12
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Hold a 12 in level horizontally against the roof (or under a rafter).
- Measure the vertical distance from the level's end to the roof.
- Enter rise and run.
- Get percent, degrees and x/12 pitch.
- Check the roofing material's minimum pitch.
Pitch conversions
| x/12 | % | Degrees |
|---|---|---|
| 3/12 | 25% | 14.0° |
| 4/12 | 33% | 18.4° |
| 6/12 | 50% | 26.6° |
| 8/12 | 67% | 33.7° |
| 12/12 | 100% | 45.0° |
Worked example: 6 in rise in 12 in run
- 6 ÷ 12 = 50%
- arctan 0.5 = 26.57°
→ 6/12 pitch, 26.6°, 50%.
Common mistakes
- Thinking 100% is 90° (it's 45°).
- Measuring along the slope instead of level.
- Installing shingles below their minimum pitch.
Pro tips
- Measure in several spots — old roofs sag.
- A digital level or inclinometer app reads degrees directly.
- Confirm your shingles or tiles allow that pitch.
- Above 12/12 you need extra fastening.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- What is a 4/12 pitch in degrees?
- 18.4°.
- Minimum pitch for shingles?
- 2/12 with special underlayment; 4/12 standard.
- What does 6/12 mean?
- 6 inches of rise per 12 inches of run.
- How many degrees is a 12/12 pitch?
- 45°.
- What is a typical roof pitch?
- 4/12 to 9/12 on most US homes.
- How do I measure pitch from inside?
- In the attic, hold the level under a rafter.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.