How to use
- Enter a vertical rise and the horizontal distance over which that rise occurs.
- Keep both measurements in the same system; US mode uses inches and metric uses centimeters.
- Optionally enter the horizontal projected area of the roof, including any overhang area you intend to count.
- Calculate to compare the pitch ratio, angle, slope percentage, and surface-area factor.
How the estimate is calculated
Let slope = rise ÷ run. Pitch per 12 is slope × 12, percent slope is slope × 100, and angle is arctan(slope). The area factor is √(1 + slope²). For a roof with uniform slope, multiply horizontal roof footprint by this factor to estimate the sloped surface area.
Example: rise 12 in over a horizontal run of 12 in gives 12.00 / 12 pitch, 45.00°, a 100.00% slope, and a 1.4142 area multiplier. With a 1,000 sq ft horizontal footprint, the calculated roof area is 1,414.2 sq ft.
Pitch conversion table
| Pitch | Angle | Area factor |
|---|---|---|
| 1/12 | 4.76° | 1.0035 |
| 2/12 | 9.46° | 1.0138 |
| 3/12 | 14.04° | 1.0308 |
| 4/12 | 18.43° | 1.0541 |
| 5/12 | 22.62° | 1.0833 |
| 6/12 | 26.57° | 1.1180 |
| 7/12 | 30.26° | 1.1577 |
| 8/12 | 33.69° | 1.2019 |
| 9/12 | 36.87° | 1.2500 |
| 10/12 | 39.81° | 1.3017 |
| 11/12 | 42.51° | 1.3566 |
| 12/12 | 45.00° | 1.4142 |
Every row is computed from the geometry above, without a roof-covering assumption. A 6/12 pitch, for example, means a rise equal to half the run; it does not mean a 6-degree angle.
Reading a level and tape measurement
From a secure accessible location, a level establishes a horizontal reference. The run is measured horizontally along that reference, while rise is measured vertically to the roof line. The sloping distance along a rafter is neither of those two inputs. If access is unsuitable, use drawings or ask for measurements rather than attempting to reach the roof.
The optional footprint is a projection, not already-measured roof surface area. Mixed pitches need separate calculations for each projected section. This tool does not add an overhang or a shingle waste allowance; the roofing calculator handles those ordering inputs.
Common mistakes
- Using sloping rafter length as run changes the ratio and understates pitch.
- A percent slope is rise divided by run times 100; a 100% slope is 45°, not 90°.
- Multiplying a measured sloped area by the factor again counts the slope adjustment twice.
Sources
Pitch, angle, and area-factor formulas: right-triangle geometry, calculated directly for this page. Follow your selected roof-covering product’s slope instructions separately.
Related calculators
- Roofing Calculator — convert footprint and pitch to bundles
- Square Footage Calculator — total projected shapes
Frequently asked questions
Can rise and run be metric?
Yes. Both fields switch to centimeters, so their ratio stays unchanged. The output pitch is still expressed as rise per 12 units of run.
What does a 6/12 pitch mean?
The roof rises 6 units vertically over 12 units horizontally. Its slope is 50%, and its angle is about 26.57 degrees.
Can I use the multiplier for a hip roof?
A uniform pitch can use the same total projected-area factor. Different pitches require separate projected sections, and material waste is another calculation.
Does this tell me whether shingles are suitable?
No. Roof-covering suitability depends on the product, roof assembly, and applicable requirements. Check those directly.