What does roof pitch mean?

Roof pitch describes the steepness of a roof as a ratio of vertical rise to horizontal run. In the US, it is expressed as X:12, meaning the roof rises X inches for every 12 inches of horizontal run. A 6:12 pitch rises 6 inches per foot of run.

How do I convert pitch to degrees?

Use the formula: angle = arctan(rise / run). For a 6:12 pitch that is arctan(6/12) = arctan(0.5) ≈ 26.57°. This calculator does the conversion instantly.

What is a standard roof pitch?

The most common residential roof pitches range from 4:12 to 9:12. Pitches below 3:12 are considered low-slope and require special underlayment. Pitches above 12:12 are considered steep-slope.

How is rafter length calculated?

Rafter length = √(rise² + run²), which is the hypotenuse of the right triangle formed by the rise and run. Add extra length for overhang, ridge board, and bird's mouth cut when ordering lumber.

What is the rafter length multiplier?

The multiplier is the rafter length divided by the run (hypotenuse / adjacent). Multiply your run by this factor to get rafter length for any span without recalculating. For a 6:12 pitch the multiplier is ≈ 1.118.

What pitch is needed for asphalt shingles?

Most asphalt shingles require a minimum pitch of 2:12 (low-slope install with double underlayment) or 4:12 for standard installation. Always check the manufacturer's specification for the product you are using.

Roof Pitch Calculator

Name: Roof Pitch Calculator
Availability: InStock
Author: Nham Vu

Calculate roof pitch (rise/run ratio), angle in degrees, and rafter length from rise and run measurements.

Roof Measurements

Rise (inches)

Vertical height from top plate to ridge.

Run (inches)

Horizontal distance from wall to below ridge. For a 6:12 pitch enter 12.

Rafter Span (inches, optional)

Enter your actual run distance to calculate exact rafter length.

Results

Enter rise and run, then press Calculate

Roof Pitch Diagram

Diagram updates after you calculate.

Common Pitch Reference

Pitch (X:12)	Degrees	Slope %	Classification

Summary

Calculate roof pitch (rise/run ratio), angle in degrees, and rafter length from rise and run measurements.

How it works

Enter the rise — the vertical height from the top plate to the roof ridge.
Enter the run — the horizontal distance from the wall to directly below the ridge (half the span).
Select your unit system (imperial or metric).
Click Calculate to get pitch ratio, degrees, percentage slope, and rafter length.
Optionally enter a rafter span to compute the exact board length needed.

Use cases

Determining roof pitch before purchasing roofing materials.
Converting an existing pitch ratio (e.g. 6:12) to degrees for framing calculations.
Estimating rafter lumber length for new construction or additions.
Verifying roof slope meets minimum drainage requirements for roofing products.
Comparing different pitch options when designing a new home.
Calculating the slope percentage for drainage planning and water runoff.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu