Roof Pitch Calculator: Pitch to Degrees, %, Rafter Length
Convert between standard roof pitch (x:12), angles in degrees, percent slope, and rise/run dimensions. Calculate common rafter lengths and cut angles.
Rafter Length & Cut Calculator
Calculate common rafter length, total rise, and layout angles. (Note: saw bevels are for hip/valley/jack rafters).
Seat: 26.57°
How to Use This Tool
- Select your input method using the tabs: Pitch (x:12), Rise/Run, Degrees, or % Slope.
- Enter your values. The tool instantly synchronizes all equivalent measurements.
- For rafters, enter your span and overhang in the section below to calculate the exact lumber length and layout angles.
- Check the dynamic diagram and copy or share your results.
Understanding Roof Pitch vs. Slope
In North America, roof incline is most commonly expressed as pitch (x:12)—the vertical rise in inches for every 12 inches of horizontal run. This convention is used in framing, roofing, and building codes.
Key distinction: True roof pitch equals rise divided by span (the full building width), while the x:12 figure represents slope (rise divided by run, or half the span). In practice, carpenters and roofing professionals use "pitch" and "slope" interchangeably when quoting x:12 ratios.
Angles in degrees or percent slope are standard in civil engineering and surveying. This calculator lets you convert freely between all three conventions.
Need to figure out pitch from an existing building? You can measure pitch from a photo using our image tool. Alternatively, use our general slope calculator for gradients, or the stair angle calculator if you're building stairs.
Roof Area Multiplier and Loads
The rafter factor or roof area multiplier lets you calculate the total surface area of a pitched roof from its flat footprint. Simply multiply the horizontal area (including overhangs) by the rafter factor.
Example: Roof Area Calculation
If your home's footprint (including eaves) is 1,000 square feet, and you have a 6:12 pitch, the rafter factor is 1.1180. Multiply 1,000 × 1.1180 = 1,118 square feet of actual roof surface area. This is essential for ordering shingles or metal panels.
Keep in mind that steep pitches shed water and snow more quickly, but the structural capacity of a roof is designed per engineered loads regardless of the pitch. (See also: solar panel tilt angles).
Standard Roof Pitch Reference Table (1:12 to 12:12)
Mathematical conversions and IRC building code underlayment specifications.
| Pitch (x:12) | Angle | Slope (%) | Rafter Factor | Rafter / 10ft Run | Code & Material Guidance | Notes & Safety |
|---|---|---|---|---|---|---|
| 1:12 | 4.76° | 8.33% | 1.0035 | 10.03 ft | Asphalt shingles prohibited (IRC R905.2). Built-up/membrane only. | Low Slope |
| 2:12 | 9.46° | 16.67% | 1.0138 | 10.14 ft | Asphalt shingles require double underlayment (IRC R905.2). | Low Slope |
| 3:12 | 14.04° | 25.00% | 1.0308 | 10.31 ft | Asphalt shingles require double underlayment (IRC R905.2). | Low Slope |
| 4:12 | 18.43° | 33.33% | 1.0541 | 10.54 ft | Standard single underlayment permitted (IRC R905.2). | Conventional Pitch (OSHA fall protection required >= 4:12) |
| 5:12 | 22.62° | 41.67% | 1.0833 | 10.83 ft | Standard materials permitted. | Conventional Pitch |
| 6:12 | 26.57° | 50.00% | 1.1180 | 11.18 ft | Standard materials permitted. | Conventional Pitch |
| 7:12 | 30.26° | 58.33% | 1.1577 | 11.58 ft | Standard materials permitted. | Conventional Pitch |
| 8:12 | 33.69° | 66.67% | 1.2019 | 12.02 ft | Standard materials permitted. | Moderate Steep |
| 9:12 | 36.87° | 75.00% | 1.2500 | 12.50 ft | Standard materials permitted. | Steep Pitch |
| 10:12 | 39.81° | 83.33% | 1.3017 | 13.02 ft | Standard materials permitted. | Steep Pitch |
| 11:12 | 42.51° | 91.67% | 1.3566 | 13.57 ft | Standard materials permitted. | Very Steep Pitch |
| 12:12 | 45.00° | 100.00% | 1.4142 | 14.14 ft | Standard materials permitted. | True 45° Pitch |
Measure Roof Pitch from a Photo
Don't have access to your attic or roof? You can estimate roof pitch from a ground-level photo using our Angle from Photo Tool. Upload or snap a photo of your roof, then use the protractor overlay to measure the angle between the roof surface and the horizon.
For the most accurate photo measurement, try to capture the roof from a distance that makes the eave line clearly visible, and avoid extreme perspective angles.
Related Angle Tools & Calculators
Explore complementary digital instruments for measuring, converting, and calculating angles.
Interactive Angle Finder
Measure angles on diagrams or interactive grid with live 0.1° digital readout, loupe magnifier, angle snap, and annotated PNG export.
Online Protractor
Measure angles on-screen or over images using an interactive digital protractor with 0.1° resolution, angle snap, and dual degree/radian readouts.
Angle from Photo Tool
Load images from file picker, camera, drag-and-drop, or paste. 100% client-side privacy—your image never leaves your device.
Angle Calculator & Converter
Convert degrees, radians, gradians, and turns. Calculate complementary, supplementary, and reflex angles with trigonometric ratios.
How We Calculate
Pitch angles and slope percentages are calculated using trigonometric arctangent relations (θ = arctan(rise ÷ run)) and standard right-triangle geometry. Rafter lengths apply the Pythagorean theorem √(rise² + run²) with ridge deductions.
Last updated: 2026-09-22 • Reviewed by [TODO: Add Reviewer - Roof framing expert] • Verified against IRC building code standards.