Roof Pitch Calculator
Convert between roof pitch (x/12), angle in degrees and slope percentage, with rafter length factor and a live diagram.
Last reviewed by the Radiatus Cloud team
Pitch is expressed as rise per 12 units of horizontal run (e.g. 6/12). The rafter multiplier converts horizontal area to actual roof surface area.
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Convert between the three ways to describe a roof
Roof steepness is expressed three different ways depending on who is talking: builders use pitch as a rise over twelve (like 4/12), designers use the angle in degrees, and some specs use slope as a percentage. This calculator converts between all three and also estimates rafter length, so a roof described one way translates to whichever you need.
Why the same roof has three numbers
Pitch as x/12 is a ratio: how many units the roof rises for every twelve of horizontal run. The angle is that ratio expressed as degrees. The slope percentage is the rise over run as a percentage. They describe the identical roof, but each trade settled on its own convention, so a plan in degrees and a builder thinking in twelfths need translating. The rafter length follows from the same geometry, since it is the hypotenuse over the run and rise.
Practical for building and estimating
Whether you are reading plans, ordering materials, or checking that a design and a build agree, converting pitch cleanly avoids the errors that come from eyeballing the equivalence. The calculation runs in your browser, so your project figures are not uploaded.
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Frequently Asked Questions
What does a pitch like 4/12 mean?
The roof rises 4 units for every 12 units of horizontal run. It is a ratio expressing steepness, common among builders.
How does pitch relate to degrees?
The angle in degrees is the pitch ratio expressed as an angle. A 4/12 pitch and its degree equivalent describe the identical roof, just in different conventions.
What is slope percentage?
The rise divided by the run expressed as a percentage, another way to state the same steepness used in some specifications.
How is rafter length found?
From the same geometry: the rafter is the hypotenuse of the triangle formed by the run and the rise, so it follows once the pitch is known.
Is my input uploaded?
No. The calculation runs entirely in your browser.
Privacy & Security
Runs entirely in your browser. No data is sent to any server.
How to Use
Enter rise and run, an angle, or a pitch value — the other measures, the rafter multiplier and a scale diagram update instantly.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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