Free · No signupPitch, degrees & multiplierActual roof area included
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Vertical height per 12 inches of run
Horizontal run (standard = 12)
Used to calculate actual roof surface area
How to Calculate Roof Pitch
Roof pitch is the ratio of the vertical rise to the horizontal run, always expressed per 12 inches of run in the US. The three values this calculator produces from a single rise/run input are:
Pitch: Rise / Run (e.g. 6/12)
Angle: arctan(Rise / Run) x (180 / pi) in degrees
Multiplier: sqrt(Rise² + Run²) / Run
Roof Area: Floor Footprint x Multiplier
Step-by-step measurement from the ground:
1. Stand at the gable end of the house
2. Measure the total width of the building and divide by 2 to get the run (horizontal distance from wall to peak)
3. Measure the vertical height from the top of the wall plate to the roof peak
4. Divide height by run to get the pitch ratio: height / run = Rise/12
5. Example: 30 ft wide building with 7.5 ft peak height: run = 15 ft, ratio = 7.5/15 = 0.5 = 6/12 pitch
Once you know the actual roof surface area, the Asphalt Calculator shows how the same area-times-multiplier approach applies to tonnage estimates for asphalt shingle or metal panel projects.
How to Calculate Roof Pitch in Degrees
Degrees are used in architectural drawings and structural specifications, while Rise/12 notation is used in the roofing trade. The formula is: Angle = arctan(Rise / Run) x (180 / pi). Every common Rise/12 pitch has an exact degree equivalent:
Pitch (Rise/12)
Angle (degrees)
Multiplier
Category
Material
1/12
4.8°
1.003
Nearly flat
Membrane only
2/12
9.5°
1.014
Low slope: requires special materials
Membrane only
3/12
14.0°
1.031
Low slope
Special shingles
4/12
18.4°
1.054
Standard residential
Standard shingles
5/12
22.6°
1.083
Standard residential
Standard shingles
6/12
26.6°
1.118
Moderate
Standard shingles
8/12
33.7°
1.202
Steep
Standard shingles
12/12
45.0°
1.414
Very steep
Standard shingles
To convert degrees back to Rise/12: Rise = tan(degrees) x 12. For a 26.6 degree roof: tan(26.6) x 12 = 0.5 x 12 = 6, which is a 6/12 pitch. This calculator shows both values automatically from a single rise/run entry.
How to Calculate Roof Area with Pitch
The actual roof surface area is always larger than the floor footprint because the slope adds length. The pitch multiplier converts footprint to actual area. Ordering roofing materials without applying the multiplier will result in a shortage:
Actual Roof Area = Floor Footprint x Pitch Multiplier Multiplier = sqrt(Rise² + 12²) / 12 Roofing Squares = Actual Area / 100 1 square = 100 sq ft of roofing material
Footprint
Pitch
Multiplier
Actual Area
Squares (+10% waste)
1,000 sq ft
4/12
1.054
1,054 sq ft
12 squares
1,000 sq ft
6/12
1.118
1,118 sq ft
13 squares
1,000 sq ft
8/12
1.202
1,202 sq ft
14 squares
1,500 sq ft
5/12
1.083
1,624 sq ft
18 squares
2,000 sq ft
6/12
1.118
2,236 sq ft
25 squares
2,000 sq ft
8/12
1.202
2,404 sq ft
27 squares
For calculating the floor footprint of your home before applying the multiplier, the Square Footage Calculator handles rectangles, L-shapes, and irregular layouts with unit conversion built in.
Shed and Lean-To Roof Pitch Calculator
Sheds, lean-tos, and single-slope (mono-pitch) roofs use the same formula as standard roofs. The key difference is that a lean-to has only one slope rather than two mirrored slopes. Use the full width of the lean-to as the run when calculating:
Structure
Recommended Pitch
Notes
Small storage shed
3/12 to 4/12
Minimum for adequate drainage with metal or shingles
Large shed or barn
4/12 to 6/12
Allows loft space, good for snow load shedding
Lean-to / porch cover
2/12 to 4/12
Lower pitch keeps the structure low at the back wall
Bike or equipment cover
2/12 to 3/12
Minimal height, use metal or polycarbonate panels
Greenhouse lean-to
3/12 to 5/12
Enough slope to run rainwater off polycarbonate
Carport / car shelter
3/12 to 4/12
Clear span with adequate drainage
For calculating materials for the interior of a shed (insulation, drywall panels, or wall sheeting), the Drywall Calculator accounts for wall area, doors, windows, and waste factor.
Example Calculation
A 1,500 sq ft ranch home has a 5/12 roof pitch. How many roofing squares should be ordered?
Each bundle of standard 3-tab shingles covers about 33 sq ft, so 18 squares = 54 bundles. Architectural/dimensional shingles are slightly different at about 25 sq ft per bundle, so check your specific product coverage before ordering.
Common Mistakes to Avoid
Using floor area as roof area
The floor footprint is always smaller than the actual roof surface. A 6/12 roof over a 1,000 sq ft footprint has 1,118 sq ft of actual surface. Always apply the pitch multiplier before ordering materials.
Confusing pitch notation with angle
A 6/12 pitch is 26.6 degrees, not 50% (which would imply a 6/12 = 50%). The rise-over-run ratio (6/12 = 0.5) is not the same as the angle. Always convert explicitly with the arctan formula or this calculator.
Ignoring valleys, hips, and dormers
Complex roofs with multiple planes have more surface area than a simple calculation suggests. Add 15-20% waste rather than 10% when the roof has intersecting planes.
Ordering by floor area without the multiplier
Many homeowners order shingles based on the floor plan rather than the actual sloped roof area. On a 6/12 roof this leads to an 11.8% material shortage before waste is even considered.
Skipping the waste factor on the order
A calculated area of 1,624 sq ft is never what you order. Cuts at ridges, valleys, edges, and hips all produce waste. For a simple gable roof add 10%; increase to 15-20% for complex shapes.
Frequently Asked Questions
Roof pitch is the ratio of vertical rise to horizontal run, expressed as Rise/12. A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. In the US roofing trade, the run is always expressed as 12, so pitch = Rise/12. In architecture and engineering, the same measurement is often expressed as an angle in degrees: 6/12 = 26.6 degrees.
Source for the 4/12 minimum pitch requirement for standard asphalt shingles and low-slope material specifications.
HR
Hassaan Rasheed
Developer and Researcher, CalculatorFlux
Researches and verifies the formulas, methodology, and source data behind each calculator on CalculatorFlux. All tools are built and checked against the cited references before publication.
Last updated: May 2026
Pitch Reference
Pitch
Angle
Mult.
1/12
4.8°
1.003
2/12
9.5°
1.014
3/12
14.0°
1.031
4/12
18.4°
1.054
5/12
22.6°
1.083
6/12
26.6°
1.118
8/12
33.7°
1.202
12/12
45.0°
1.414
Pro Tip
When ordering roofing materials, add 10-15% waste to your calculated area. For complex roofs with hips, valleys, or dormers, use 15-20%. The results card already shows squares with 10% applied when you enter your footprint.