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Roof pitch calculator

Convert roof measurements into pitch, angle, and rafter length

Choose the measurements you know. The calculator resolves the roof triangle, shows the geometry, and converts it to X-in-12 pitch, degrees, percentage, and common-rafter length.

1 · Enter known measurements

Roof triangle details

Measurement display
What measurements do you know?
Rise and run
in
in
in
Full outside-to-outside span; the calculator uses half for one common rafter.

2 · Review the roof geometry

Your roof-pitch result

Calculated resultStandard roof pitch6 in 12Conventional roof slope
Angle
26.57°
Slope
50.0%
Common rafter
161 in
Rafter factor
1.1180
Roof-pitch right-triangle diagramRight-triangle roof section with 72 in rise, 144 in run, 26.57 degree angle, and 161 in rafter length.26.57°Run: 144 inRise: 72 inRafter: 161 in
Right-triangle roof section with 72 in rise, 144 in run, 26.57 degree angle, and 161 in rafter length. Diagram is proportional and excludes overhang and cut details.

Calculated triangle

Rise
72 in
Run
144 in
Building span
288 in
Common-rafter length
161 in
Length per unit of run
1.1180

Common pitch conversion table

Rafter factor is the sloped length for each unit of horizontal run.

PitchAngleSlopeRafter factor
1:124.76°8.3%1.0035
2:129.46°16.7%1.0138
3:1214.04°25.0%1.0308
4:1218.43°33.3%1.0541
5:1222.62°41.7%1.0833
6:1226.57°50.0%1.1180
7:1230.26°58.3%1.1577
8:1233.69°66.7%1.2019
9:1236.87°75.0%1.2500
10:1239.81°83.3%1.3017
11:1242.51°91.7%1.3566
12:1245.00°100.0%1.4142

Formula and assumptions

pitch rise per 12 = (rise ÷ run) × 12
angle = arctangent(rise ÷ run)
rafter = √(rise² + run²)
  • The roof is modeled as one right triangle from the exterior wall line to the ridge centerline.
  • Building span is split equally for a symmetrical gable roof with the ridge centered over the span.
  • Calculated common-rafter length excludes overhang, ridge-board adjustment, birdsmouth cuts, tails, and field allowances.
  • Pitch classification is general terminology, not a product, structural, or code determination.
Measure Plan BuildGenerated https://measureplanbuild.com/calculators/roof-pitch

Geometry estimate only. Verify field measurements, safe access, structural design, product instructions, and current local requirements.

What the roof-pitch result means

X-in-12 pitch describes vertical rise for every 12 inches of horizontal run. Angle expresses the same slope in degrees, while slope percentage is rise divided by run multiplied by 100. The rafter factor is the sloped length required for each unit of horizontal run.

Safety first: Roof measurement and access can cause severe injury or death. Use drawings, attic framing, a gable end, or a qualified professional whenever those options avoid climbing onto the roof.

How to use the roof-pitch calculator

  1. Select the pair of measurements you can verify reliably.
  2. Choose one unit for every length measurement.
  3. Enter the full building span, not the single-slope run, when span is requested.
  4. Review the pitch, angle, slope percentage, and proportional triangle.
  5. Use the common-rafter value only as geometry, then add project-specific details.
  6. Print or copy the result and verify it against drawings and field dimensions.

Roof-pitch formulas

A roof section is a right triangle. Rise is vertical, run is horizontal, and the common rafter is the hypotenuse.

pitch rise per 12 = (rise ÷ run) × 12
angle = arctangent(rise ÷ run)
slope percentage = (rise ÷ run) × 100
common rafter = √(rise² + run²)

Worked 6-in-12 example

A measured rise of 6 inches over a 12-inch run produces a 6-in-12 pitch. The angle is approximately 26.57 degrees and the slope is 50%. On a symmetrical building with a 24-foot span, one roof run is 12 feet and the plate-to-ridge rise is 6 feet.

The geometric common-rafter line is about 13 feet 5 inches before any ridge adjustment, overhang, birdsmouth, tail, or cutting allowance is added.

Common roof-pitch mistakes

  • Using the full building span as the run instead of dividing a centered gable in half.
  • Measuring along the roof surface when the formula needs horizontal run.
  • Confusing a 50% slope with a 50-degree roof angle.
  • Assuming the geometric rafter length includes overhang and framing cuts.
  • Taking unsafe roof measurements when an attic, gable, or plan is available.
  • Using pitch alone to choose structural member sizes or roofing products.

Frequently asked questions

How do I convert rise and run to roof pitch?

Divide rise by run, then multiply by 12. A roof that rises 6 inches over a 12-inch horizontal run is a 6-in-12 pitch.

What angle is a 6-in-12 roof pitch?

A 6-in-12 pitch has an angle of about 26.57 degrees and a slope of 50 percent.

Does the rafter result include the overhang?

No. The common-rafter result runs from the exterior wall line to the centered ridge. It excludes overhang, ridge-board adjustment, birdsmouth cuts, tails, and field allowances.

Can I measure roof pitch without climbing onto the roof?

Often, yes. Pitch may be measured from accessible attic framing, a gable end, construction drawings, or with suitable ground-based methods. Avoid roof access unless you have appropriate equipment and experience.

Is roof pitch enough to size rafters?

No. Rafter sizing depends on loads, species and grade, spacing, spans, connections, roof assembly, local requirements, and an approved structural design.

Keep planning safely

Read How to Measure Roof Pitch Safely, or return to all DIY calculators.

Measurement and safety disclaimer

This tool provides geometric planning estimates, not structural engineering, fall protection training, product approval, or code approval. Verify field conditions, drawings, loads, member sizes, connections, roofing requirements, safe access, and current local rules. Review the full measurement disclaimer.