Roof Pitch Calculator
Horizontal distance from the ridge center to the eave (half the building width for a gable roof)
Vertical height from the wall plate to the ridge at the run distance
Horizontal eave overhang beyond the exterior wall — added to rafter length
Roof Area Estimator (optional)
Cost per square foot (or square meter) of roofing material for a project cost estimate
Enter Roof Measurements
Enter your run and rise (or angle, slope %, or pitch ratio) to instantly see the pitch ratio, angle, rafter length, framing cut angles, and more.
How to Use This Roof Pitch Calculator
Choose Your Input Mode
Select how you know your roof slope: Rise + Run (the most common method), Angle in degrees, Slope Percentage, or the X:12 Pitch Ratio. Use the Quick Pick buttons to instantly load common pitches like 4:12, 6:12, or 12:12. Choose Imperial (inches/feet) or Metric (meters) using the unit toggle.
Enter Your Measurements
Type your run (horizontal distance from ridge to eave) and the corresponding rise or slope value. For a gable roof, run is half the building width. Optionally enter the eave overhang distance to get the extended rafter length including the overhang. All values auto-calculate as you type.
Read Your Results
The visual triangle diagram updates live to show your roof geometry. Read the pitch ratio (X:12), degrees, slope percentage, rafter length, plumb cut angle, and seat cut angle. The pitch comparison bar shows where your slope falls relative to standard, steep, and extreme ranges. Check the walkability, material, and snow-shedding guidance below.
Estimate Roof Area and Export
Enter your building footprint dimensions (length and width) in the Roof Area Estimator section to calculate the true sloped surface area. Add a material cost per square unit for an instant project cost estimate. Use Export CSV to save all values, or Print Results for a formatted summary to bring to the job site.
Frequently Asked Questions
What is the most common roof pitch for residential homes?
In North America, the most common residential roof pitch is 6:12, which means the roof rises 6 inches for every 12 inches of horizontal run — equivalent to about 26.6 degrees. This pitch offers a good balance: it sheds rain and snow effectively, looks proportional on most home styles, accommodates all standard roofing materials including asphalt shingles and metal, and falls within the 4:12 to 9:12 range that most roofing contractors consider standard. Pitches from 4:12 to 7:12 are considered moderate and make up the majority of new residential construction in the continental United States.
What is the minimum roof pitch for asphalt shingles?
The minimum roof pitch for standard asphalt shingle installation is 4:12 (about 18.4 degrees). At slopes of 3:12 to 4:12, most shingle manufacturers allow installation only with a double layer of underlayment or a specific low-slope application method, as specified in their installation instructions. Below 3:12 (14 degrees), asphalt shingles are generally not recommended at all and waterproofing membranes such as modified bitumen, EPDM, or TPO are required. Always check the specific manufacturer guidelines and local building code requirements for your area, as requirements can vary.
How do I measure roof pitch from the ground or inside the attic?
The easiest method is from inside the attic. Hold a level horizontally against a rafter and mark exactly 12 inches along the level from the rafter. Then measure vertically from the 12-inch mark up to the rafter — that vertical measurement is your rise, giving you an X:12 pitch directly. From outside, you can hold a level against the roof slope at the eave: mark 12 inches from one end and measure vertically from the other end of the level to the roof surface. Some contractors use a speed square or digital angle finder placed flat against the roof surface to read the angle directly in degrees, which you can then enter into this calculator.
What is the difference between plumb cut and seat cut angles?
The plumb cut (also called the ridge cut or vertical cut) is the angled cut made at the top end of a rafter where it meets the ridge board. This cut is perpendicular to the earth — truly vertical — regardless of the rafter's orientation. Its angle equals 90 degrees minus the roof pitch angle. The seat cut (also called the bird's mouth or level cut) is the notch near the bottom of the rafter that sits flat on top of the wall plate. Its horizontal face must be perfectly level, and its angle equals the roof pitch angle itself. Both are set on a circular saw bevel scale. This calculator shows both angles directly from your pitch input.
What roof pitch is needed for good snow shedding?
The widely accepted minimum pitch for reliable snow shedding is 6:12 (26.57 degrees). At this slope, most snowfall will slide off the roof rather than accumulating. For regions with very heavy snowfall — such as the northern Rockies, Great Lakes snowbelt, or parts of New England — many engineers and building codes recommend 7:12 or steeper. Below 4:12, roofs in heavy snow regions need to be engineered for the additional structural loads of accumulated snow, since the snow will not shed efficiently. Metal roofs are especially effective at shedding snow due to their low surface friction, while rough-textured materials like asphalt shingles hold snow longer.
How does roof pitch affect the amount of roofing material I need?
The higher the pitch, the more actual roof surface area you have compared to the footprint area below. The roof area multiplier (pitch factor) quantifies this relationship. A flat 1:12 roof has a multiplier of 1.003 — almost no extra area. A standard 6:12 has a multiplier of 1.118, meaning you need about 11.8% more material than the footprint. A steep 12:12 (45 degrees) multiplier is 1.414, requiring 41% more material than the horizontal area. Multiply your building footprint (length times width) by the area multiplier to get the true sloped surface area. Always order an additional 10 to 15 percent extra for waste from cutting around valleys, hips, eaves, and penetrations.