The Roof Pitch Calculator is a free online tool that instantly computes roof pitch ratio, angle in degrees, slope percentage, and rafter length from rise and run measurements.
What is the Roof Pitch Calculator?
The Roof Pitch Calculator calculates pitch ratio (e.g., 4:12), corresponding degrees, slope percentage, and rafter length using user-supplied rise (inches) and run (inches). An optional roof span (feet) refines rafter length for a full gable roof. Results update in real time on a diagram, and the tool includes a reference chart of 12 common pitches. It runs in any web browser and is provided by RoofAngler.
Key Features
- Rise & Run Input — enter rise and run in inches; the calculator instantly returns pitch ratio, degrees, slope percentage, and rafter multiplier.
- Optional Roof Span — input the full width of the roof in feet to calculate total rafter length for a gable roof.
- Interactive Diagram — a visual roof diagram updates as values are entered, showing the pitch angle and rafter length.
- Common Pitches Reference Chart — table of 12 pitches from 1:12 to 16:12, including degrees, slope percentage, rafter multiplier, pitch category (flat/low/conventional/steep), and typical uses (e.g., 4:12 minimum for asphalt shingles).
- Frequently Asked Questions — answers to eight roof-pitch questions, covering calculation methods, conversion to degrees, minimum pitch for shingles, and attic measurement.
- Related Articles — links to three RoofAngler blog posts: Shed Roof Pitch Calculator, How Do I Calculate Roof Pitch?, and How to Calculate Roof Pitch Factor.
Who is it for?
- Homeowners and DIYers checking whether their roof meets the minimum pitch for asphalt shingles (4:12) or other roofing materials.
- Contractors and roofers calculating rafter lengths for a gable roof using the span input, and referencing the rafter multiplier for material estimates.
- Architects and designers converting pitch to degrees or slope percentage for plan drawings, and comparing their intended pitch against common residential categories (e.g., 6:12 most common residential).
What can you do with the Roof Pitch Calculator?
- Determine pitch from measurements — input rise and run in inches to get the pitch ratio (e.g., 7:12) and its degree equivalent (30.26°).
- Calculate rafter length — add the roof span in feet to get the actual rafter length including the multiplier (e.g., 8:12 pitch gives a multiplier of 1.2019).
- Visualize roof geometry — view an automatically updated diagram that shows the slope, rafter, and span based on entered values.
How does it work?
Enter the rise (vertical height in inches) and run (horizontal distance in inches) into the two input fields. Optionally enter the roof span in feet for rafter length. The calculator immediately displays the pitch ratio, degrees, slope percentage, and rafter length. The diagram updates to reflect the entered values. A reset button clears all fields, and a copy button copies results.
Pricing
The Roof Pitch Calculator is free to use with no tiers or limitations.
FAQ
What is roof pitch?
Roof pitch is the ratio of vertical rise to horizontal run, expressed as “X:12” (e.g., 4:12 means 4 inches of rise per 12 inches of run). It determines the roof’s steepness and affects material choices and drainage.
How do I calculate roof pitch?
Measure the vertical rise in inches over a 12-inch horizontal run. Divide rise by run and simplify to “rise:12”. The calculator does this automatically when you input rise and run.
What is the minimum roof pitch for asphalt shingles?
According to the reference chart, the minimum pitch for asphalt shingles is 4:12 (18.43°). Lower pitches require membrane or modified bitumen roofing.
