Convert roof pitch, angle, rise, run, and rafter length for a simple roof measurement.
Enter a pitch and an optional horizontal run for each scenario. All scenarios share the same unit system.
Results
Estimated Roof Pitch
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Right triangle: rise (vertical) + run (horizontal) = rafter (hypotenuse)
| Metric | Value | How Calculated |
|---|
Based on published slope references. Local code, manufacturer instructions, roof assembly details, and professional judgment control. Verify all material choices independently.
| Pitch Range | Material Categories to Investigate | Notes & Cautions |
|---|
Comparing multiple pitch scenarios for the same horizontal run. A steeper pitch increases rafter length and roof surface area. Confirm design choices with a qualified roofing professional.
| Scenario | Pitch | Angle | Slope % | Rafter Length | Multiplier | Material Category |
|---|
Rafter Length Comparison
Choose a measurement method and enter the values you have. Each method converts your input into the same set of pitch, angle, slope, and rafter results.
Roof pitch describes how steep a roof is. In residential construction, it is written as a ratio such as 6:12, meaning the roof rises 6 units vertically for every 12 units of horizontal run.
The same steepness can be expressed in several formats:
Roof pitch matters because it affects drainage, roof appearance, roof surface area, material options, access difficulty, and framing measurements. A small pitch change can make a noticeable difference in rafter length and roof surface area.
This calculator uses geometry. It does not design a roof structure, size rafters, confirm load capacity, evaluate roof condition, inspect drainage, check permits, or replace a qualified roofing professional. Results are estimates for planning and informational purposes only.
The material compatibility guidance is based on published slope references from sources including the 2024 International Residential Code Chapter 9, NRCA slope guidance, and the Asphalt Roofing Manufacturers Association. Local codes, manufacturer instructions, roof assembly details, and professional judgment can change what is appropriate for a specific roof.
All calculations are based on right-triangle geometry. Rise, run, and rafter form a right triangle.
Pitch ratio: rise ÷ run
Pitch x:12: (rise ÷ run) × 12
Angle: arctan(rise ÷ run) — using the inverse tangent function. See Mathematics LibreTexts and Clark University Math for background on the tangent and arctangent relationships.
Slope percentage: (rise ÷ run) × 100
Rafter length — the hypotenuse of the right triangle, calculated using the Pythagorean theorem:rafter = √(rise² + run²)
Roof surface multiplier: √(1 + pitchRatio²)
Simple gable roof area: roof length × rafter length to ridge × 2
Sloped overhang: horizontal overhang ÷ cos(angle)
A roof has a 6:12 pitch and a 10-foot horizontal run.
For a 24-foot span (12-foot run each side) with 6:12 pitch:
Note on material guidance: The material compatibility table is not a pure formula. It is an interpretation layer based on published roof slope references and industry guidance. Local code, manufacturer instructions, underlayment requirements, and professional judgment control what is appropriate for a specific roof.
| Output | Rounding |
|---|---|
| Pitch (x:12) | 2 decimal places |
| Angle | 1 decimal degree |
| Slope percentage | 1 decimal percent |
| Roof surface multiplier | 3 decimal places |
| Rafter length (imperial) | Nearest 1/16 inch in feet and inches; 2 decimal feet in table |
| Rafter length (metric) | Nearest millimeter (small values) or centimeter (larger values) |
| Roof area (imperial) | Nearest square foot |
| Roof area (metric) | Nearest tenth square meter |
This calculator converts roof measurements using right-triangle geometry. It first normalizes the selected input mode into a common rise/run ratio (pitch ratio). From that ratio, it calculates pitch x:12, roof angle in degrees, slope percentage, rafter line length estimate, ridge rise for simple gable roofs, and roof surface multiplier. When roof span is provided, the calculator assumes a simple centered gable roof and uses half the span as the horizontal run.
Material guidance is based on published roof slope references and should be treated as a screening tool only. Local codes, roof assembly design, climate, manufacturer instructions, underlayment requirements, drainage details, and professional judgment can change what is appropriate for a specific roof.
These resources can help you understand roof slope requirements, material specifications, safety considerations, and energy-related roofing decisions.
You can verify roof pitch from building plans, a recent inspection report, an attic measurement, or a contractor's written estimate. If you measure from inside the attic, remember that insulation, uneven framing, old roof layers, and access limits can make measurements approximate.
For roof repairs, replacements, structural changes, permitting, or material selection, confirm the numbers with a qualified roofing contractor, structural professional, manufacturer instructions, or your local building department. Do not climb onto a roof just to use this calculator. Roof access can be dangerous, and calculator results are estimates for informational purposes only.
This calculator provides estimates for informational purposes only. The Homebase Calculators Editorial Team reviews formulas, assumptions, and explanatory content for consistency and clarity. Always confirm measurements and material choices with a qualified professional and your local authority having jurisdiction.
Roof pitch describes how much a roof rises compared with its horizontal run. A 6:12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance. The same roof can also be described as an angle in degrees (about 26.6° for 6:12) or a slope percentage (50% for 6:12).
Divide the rise by the run, then multiply by 12 to convert to x:12 format. For example, a 5-inch rise over a 10-inch run equals 0.5, and 0.5 × 12 equals a 6:12 pitch. Make sure the run is horizontal — not the sloped roof surface or rafter length. Use the Rise and Run mode in this calculator to enter your measurements directly.
The calculator treats the rise, run, and rafter as a right triangle and applies the Pythagorean theorem: rafter length equals the square root of rise squared plus run squared. This gives a line-length estimate — not a finished cut list. It does not include birdsmouth cuts, ridge adjustment, or structural details.
Yes, for a simple centered gable roof. The Roof Span mode divides the total span by two to estimate the horizontal run from the wall plate to the ridge. This works well for straightforward gable roofs. Complex roofs with offset ridges, hips, valleys, dormers, or additions need more detailed layout and professional framing plans.
Low-pitch roofs usually need roofing systems specifically designed for low-slope drainage and water resistance. Some metal panel systems, membrane systems, and modified bitumen products may be possible depending on the exact slope, seam design, drainage, local code, and manufacturer requirements. Standard steep-slope shingle products should not be assumed to be suitable for very low pitches without verification. See the material guidance table in the calculator results for slope-range context.
A 2:12 pitch is at or near the minimum slope referenced by some residential code guidance for asphalt shingles, but it often requires additional underlayment layers or special installation details. The 2024 IRC Chapter 9 and the Asphalt Roofing Manufacturers Association both emphasize that local code and manufacturer instructions control whether a specific product may be used at a given slope. This calculator shows a "verify carefully" note for 2:12 — not automatic approval or rejection.
No. Pitch and angle describe the same steepness in different formats. Pitch is written as rise per 12 units of run — for example, 6:12. Angle is measured in degrees above horizontal. A 6:12 pitch equals approximately 26.6°. This calculator converts freely between the two formats and also expresses the same steepness as a slope percentage.
No. Rafter sizing depends on span, spacing, lumber species, grade, loads (live load, snow load, dead load), roof covering weight, local code, and structural design requirements. This calculator estimates rafter line length as a geometry figure only — not a structural recommendation. Use local span tables, building code references, or consult a qualified structural professional for rafter sizing.
No. Do not climb onto a roof just to take measurements for this calculator. Safer options include using the Attic Measurement mode, checking building plans or framing drawings, reviewing an inspection report, reviewing a contractor's written estimate, or asking a qualified professional. Per OSHA 29 CFR 1926.501, roof access involves real fall hazards that require proper fall protection equipment and training in professional settings. Homeowner access situations vary, but the risk is real.
Found a calculation error, outdated source, broken assumption, or something unclear on this page? Contact the Homebase Calculators Editorial Team so we can review it. We update pages when corrections are warranted.