Roof Pitch Calculator
Roof pitch is the ratio of vertical rise to horizontal run, written as X:12 (rise per 12 inches of run). Divide rise by run and multiply by 12 for the pitch, or take the arctangent of rise/run for the angle in degrees.
Quick Answer
Roof pitch is the ratio of vertical rise to horizontal run, written as X:12 (rise per 12 inches of run). Divide rise by run and multiply by 12 for the pitch, or take the arctangent of rise/run for the angle in degrees.
Roof Pitch Calculator
Enter the rise and run of your roof to get the pitch ratio, angle in degrees, and the area multiplier used to estimate roofing material for a shed or workshop roof.
Enter your values and click calculate.
How to Use This Calculator
Use a level and tape measure across a fixed 12 inch run, or read rise/run straight off building plans.
Divide rise by run and scale to a 12 inch run for the standard X:12 notation used in the US.
Steeper roofs have more actual surface area than their flat footprint — multiply footprint square footage by this factor to estimate roofing material.
Many roofing materials, including asphalt shingles, have a minimum pitch (often around 2/12 to 3/12) for warranty and drainage reasons.
Formula
Pitch = (Rise / Run) x 12. Angle (degrees) = arctan(Rise / Run) x (180 / pi). Area multiplier = sqrt(1 + (Rise/Run)^2).
Common Roof Pitches and Angles
| Pitch | Angle | Multiplier |
|---|---|---|
| 2/12 | 9.5 deg | 1.014 |
| 3/12 | 14.0 deg | 1.031 |
| 4/12 | 18.4 deg | 1.054 |
| 6/12 | 26.6 deg | 1.118 |
| 8/12 | 33.7 deg | 1.202 |
| 9/12 | 36.9 deg | 1.25 |
| 12/12 | 45.0 deg | 1.414 |
Common Mistakes to Avoid
- Confusing the pitch ratio (X:12) with a percentage slope — they are related but not the same number.
- Measuring rise and run in different units without converting first.
- Forgetting the area multiplier when ordering roofing material — the actual roof surface is always larger than the building’s flat footprint on any sloped roof.
- Ignoring the minimum pitch requirement for a chosen roofing material, which can void material warranties or cause drainage problems.
When the Estimate May Be Wrong
This calculator assumes a simple gable-style rafter measured on a straight run. Hip roofs, valleys, and complex rooflines need additional layout math beyond a single pitch figure, and any structural framing decisions should follow your local building code and span tables, not this estimate alone.
FAQs
What is a 4/12 roof pitch in degrees?
A 4/12 pitch is about 18.4 degrees from horizontal.
What is considered a steep roof pitch?
Pitches steeper than about 9/12 (roughly 37 degrees) are generally considered steep and may need special safety precautions to walk on.
How do I measure the pitch of an existing roof?
Hold a level or rafter square against the roof surface, measure the rise over a fixed 12 inch run, or use a smartphone angle/level app against the slope.
Why does roof pitch matter for a workshop or shed build?
Steeper pitches shed water and snow better but need more roofing material and steeper, longer rafters — both affect your material list and budget.
Sources and Methodology
Pitch-to-angle conversions use the standard trigonometric relationship (angle = arctan(rise/run)) and the area multiplier formula (sqrt(1+(rise/run)^2)) used throughout residential construction and roofing references as of 2026.
