Structure calculator

Roof Pitch Calculator

Read pitch, angle, rafter length, and slope factor from rise and run. Switch between US customary and metric units, adjust the assumptions, and keep every step visible.

01 Measure02 Allow03 Order

Project inputs

Use one unit system throughout. Defaults show a realistic example; replace them with measurements from your project.

Unit system

RiseExample input — replace with your project value.inRunExample input — replace with your project value.inBuilding spanExample input — replace with your project value.ftBuilding lengthExample input — replace with your project value.ftEave overhangExample input — replace with your project value.in

Measurement guideRun is horizontal. Rise is vertical. Measure the building length separately.

Measure the finished shape. This geometric estimate assumes a simple symmetrical gable roof. Structural rafter sizing, ridge details, load paths, and code compliance require qualified design.

Estimate matches the inputs shown.

ReviewedNovember 2, 2026

ByBuildGauge Editorial Team

ScopeFormula, defaults & sources

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The calculation

A visible formula, not a black box.

Pitch & angle · Mathematical derivationangle = arctan(rise ÷ run); slope factor = √(1 + (rise ÷ run)²)

Inputs are converted to a common base unit before calculation. Purchase quantities are rounded only at the final buying boundary.

Example inputDefaultStatus

Rise6 inPlanning default — verify

Run12 inPlanning default — verify

Building span24 ftPlanning default — verify

Building length36 ftReplace with measurement

Eave overhang12 inPlanning default — verify

Worked example

Example: a 6:12 roof

A 6 in rise over 12 in run gives a 26.6° angle and a 1.118 slope factor. This is geometry, not structural design.

Use this to understand the workflow—not as a recommendation for your project.

Sources & scope

What supports this calculation.

Mathematical derivationOpenStax right-triangle trigonometry ↗

The angle, slope factor, and rafter-length relationships used by the geometry model.

Common mistakes

Check the job, not just the number.

01Leaving the example roof pitch inputs unchanged instead of entering measured project values.
02Treating an editable coverage, size, density, or allowance as universal instead of checking the selected product label, project documents, and local requirements.
03Ordering from the rounded result without reviewing exclusions: This geometric estimate assumes a simple symmetrical gable roof. Structural rafter sizing, ridge details, load paths, and code compliance require qualified design.

Questions, answered

Roof pitch FAQ

What does the Roof Pitch Calculator estimate?

Read pitch, angle, rafter length, and slope factor from rise and run. The primary output is pitch & angle, with the intermediate assumptions kept visible.

How is the roof pitch result calculated?

The visible formula is: angle = arctan(rise ÷ run); slope factor = √(1 + (rise ÷ run)²). Inputs are converted to a common base unit before the final purchase boundary is rounded.

Are the default values recommendations?

No. Dimensions are worked examples and product-dependent presets are planning defaults. Replace them with the selected product label, project documents, and local requirements.

Is the result ready to order from?

Use it as a checked planning estimate, then confirm packaging, minimum orders, installation instructions, site conditions, and any code or professional-design requirements.