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Roof Pitch Calculator

Convert roof pitch rise and run to angle, percent slope, and pitch factor. Essential for roofing material estimates, rafter layout, and drainage design.

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Inputs that matter
Rise, Run
Output to expect
Roof Pitch Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Projects using Roof Pitch Calculator

This tool is part of these guided projects. Each project provides step-by-step instructions with checklists and all the tools you need in one place.

Roof Repair Decision Record

Coordinate one authorized roof repair through emergency stabilization, safe evidence capture, structural and assembly review, bounded material scenarios, controlled work, inspection, and named acceptance.

6 steps3 toolsStart project

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Reference & details

How it works

Pitch Notation

US convention expresses pitch as inches of rise per 12″ horizontal run. A 4/12 pitch rises 4″ for every 12″ of run.

Pitch = Rise ÷ Run (expressed as X/12)

Pitch Factor

Multiply footprint area by pitch factor to get true roof surface area. 4/12 pitch factor ≈ 1.054.

Pitch Factor = √(1 + (Rise/Run)²)

Angle and Percent

Convert pitch to degrees for rafter cuts and to percent slope for drainage and code minimums.

Angle (°) = arctan(Rise/Run); Slope % = (Rise/Run) × 100

Updated: July 2026

Example Scenarios

1,500 sq ft footprint × 1.054 pitch factor = 1,581 sq ft roof area for shingle and underlayment orders.

8/12 pitch equals 33.7° — use for miter saw settings on rafter tails and fascia angles.

2/12 (9.5°) is minimum for many rolled roofing products. Verify against manufacturer and local code before low-slope install.

FAQ

Most US homes use 4/12 to 6/12 pitch (18°–27°). Walkable for installation without special equipment. Steeper roofs shed water faster but cost more to shingle.

Use a 12″ level and tape: mark vertical rise at 12″ horizontal from level on underside of rafter or with pitch gauge on roof surface.

6/12 pitch factor = √(1 + 0.5²) = √1.25 ≈ 1.118. Multiply footprint by 1.118 for roof surface area.

Related but different units. 4/12 pitch = 33.3% slope (4÷12×100). Pitch uses run of 12″; percent uses run of 100 units.

Above 7/12 (30°) requires roof brackets or harness. 12/12 (45°) is extremely steep — use scaffolding and fall protection.

About Roof Pitch Calculator

Convert between roof pitch notation (rise over 12″ run), angle in degrees, and slope percent for roofing and construction. Enter rise and run to get pitch factor for converting footprint area to actual roof surface area.