Roofing / Field guide
How to Calculate Roof Pitch
Use rise and horizontal run to calculate pitch, compare common roof slopes, and plan a more realistic shingle estimate.
Last updated September 25, 2026. Methodology, sources & assumptions.
Open the Roof Pitch Calculator01 / The details
Use the roof pitch formula: rise ÷ run × 12
Roof pitch compares vertical rise with horizontal run. It is usually written as inches of rise for every 12 inches of level run. The roof pitch formula is pitch = (rise ÷ run) × 12. Measure rise and run in the same units.
For example, 6 inches of rise over 12 inches of horizontal run gives 6 ÷ 12 × 12 = 6, or a 6/12 pitch (also written 6:12). A 9-inch rise over an 18-inch run is also 6/12. Run is horizontal distance—not the diagonal length of the rafter.
- Rise is the vertical change in height.
- Run is the level, horizontal distance.
- Pitch is a ratio; it is not the roof angle in degrees.
Rise over run
A 6/12 roof rises 6 inches per 12 inches across.
Pitch per 12 in = rise ÷ run × 12
Angle (degrees) = atan(rise ÷ run) × 180 ÷ π
Area factor = √(1 + (rise ÷ run)²)
02 / The details
Compare 4/12, 6/12, and 9/12 roof pitches
For one uniform roof slope, the surface-area multiplier is √(1 + (rise ÷ run)²). Multiply the horizontal plan area by that factor for a first estimate of sloped roof area, before accounting for overhangs, openings, roof shape, or waste.
The examples below apply each pitch to the same 1,000-square-foot horizontal footprint so you can see how a steeper slope changes the starting area for a materials estimate.
Roof pitch
4/12
- Angle
- 18.4°
- Area factor
- 1.054×
- On 1,000 sq ft
- 1,054 sq ft
Roof pitch
6/12
- Angle
- 26.6°
- Area factor
- 1.118×
- On 1,000 sq ft
- 1,118 sq ft
Roof pitch
9/12
- Angle
- 36.9°
- Area factor
- 1.250×
- On 1,000 sq ft
- 1,250 sq ft
Approximate sloped area before overhangs, dormers, valleys, cuts, and waste.
03 / The details
Pitch, angle, roof area, shingles, and cost
Pitch and angle describe the same slope in different ways. Convert rise and run to degrees with angle = atan(rise ÷ run) × 180 ÷ π. For a 6/12 roof, the angle is atan(6 ÷ 12), or about 26.6°—not 6°.
A pitch-based area factor changes the roof surface area used to plan shingles and other roofing materials. Actual quantities also depend on separate roof planes, product coverage, cuts, valleys, and the waste allowance you choose. Steepness can affect access and labor, but pitch alone cannot determine a roofing quote; material, roof condition, geometry, and local pricing matter too.
04 / The details
Check measurements before estimating materials
Use plans, a safe attic measurement, or a qualified roofer rather than climbing onto the roof to measure it. If a roof has dormers, hips, valleys, overhangs, or more than one pitch, measure those areas separately; the simple multiplier does not describe every roof shape.
Once you have a reliable pitch and roof area, use the Roof Pitch Calculator for the rise/run conversion and the roofing tools for area, shingle quantity, and cost planning. Follow product instructions and local requirements; a material estimate is not a structural or code review.
- Measure horizontal run, not the sloped rafter length.
- Estimate roof planes with different pitches separately.
- Add product-specific coverage and waste assumptions after calculating area.
The short version
Pitch per 12 inches of horizontal run = rise ÷ run × 12. Apply the matching area multiplier for a first roof-surface estimate, then account for roof shape, product coverage, and waste.
Common questions
Roof Pitch FAQs
How do you calculate roof pitch?
Divide vertical rise by horizontal run, then multiply by 12. A 6-inch rise over a 12-inch level run is 6 ÷ 12 × 12 = 6, or a 6/12 pitch. Use the same units for both measurements.
What does a 6/12 roof pitch mean?
It means the roof rises 6 inches for every 12 inches of horizontal run. That ratio corresponds to an angle of about 26.6° and a surface-area multiplier of about 1.118 for a uniform slope.
How do I convert roof pitch to degrees?
Use angle = atan(rise ÷ run) × 180 ÷ π. For a pitch written as p/12, calculate atan(p ÷ 12) in degrees; 6/12 is about 26.6°.
Why does roof pitch matter for shingles?
Pitch changes the sloped roof area used to estimate shingle quantity, and product instructions may set slope limits or installation requirements. Roof steepness can also affect access and labor, so check the chosen product and local conditions.
Can I measure roof pitch from the attic?
Yes, if the attic is safe to enter. At a rafter, use a level to mark a 12-inch horizontal run and measure the vertical rise to the roof surface. Keep secure footing, do not step on ceiling drywall, and use plans or a professional if access is unsafe.
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