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Roof Pitch Calculator
Roof pitch in degrees, x-in-12 and percentage, with rafter length.
Roof Pitch Calculator tool
Height from the wall plate to the ridge.
Half the span, wall to centre.
Optional. Gives the roof area.
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Pitch
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As x in 12
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As a percentage
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Rafter length
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Roof area
| Measure | Value |
|---|
The run is half the span, not the whole width of the building. Using the full span is the commonest error here and halves the calculated pitch.
About the Roof Pitch Calculator
Roof Pitch Calculator converts between the three ways a roof slope is described and gives the rafter length that follows. Degrees in most of Europe, the x-in-12 ratio in America and carpentry, and a percentage in civil engineering -- all the same angle expressed differently.
The run is half the span, from the wall plate to the centre line under the ridge, not the full width of the building. Using the whole span halves the calculated pitch, and it is by far the most common mistake made with this calculation.
The pitch multiplier is the number worth taking away. It is one over the cosine of the pitch, and it converts a plan area into a roof area: a 26.57 degree roof has a multiplier of 1.118, so the sloping surface is about twelve per cent larger than the footprint it covers. That is the factor that decides how many tiles, how much felt and how much insulation a roof actually needs.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
Looking for something this does not cover? FreeToolsZone.org is more free browser-based tools, organised by job, and it is worth a look if roof pitch calculator is only part of what you are working on.
How to use the Roof Pitch Calculator
- Choose i know theThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
- Enter rise (m), run (m) and pitch (degrees)Decimals are fine, and thousands separators are accepted and ignored.
- Read the pitch, as x in 12 and as a percentageThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.
Features
- Shows pitch, as x in 12, as a percentage, rafter length and roof area together, so you are not running it twice
- A results table you can read across
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The roof pitch calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Converting a roof pitch between degrees and x-in-12
- Working out rafter length from rise and run
- Finding the true roof area from the plan area
- Checking a pitch against the minimum for a tile
Frequently asked questions
What is the run?
Half the span: the horizontal distance from the wall plate to the point below the ridge. Using the full span halves the pitch.
What does 6 in 12 mean?
Six units of rise for every twelve of run, which is 26.57 degrees or a 50 per cent slope. It is the American carpentry convention.
How do I get the roof area?
Multiply the plan area by one over the cosine of the pitch. The multiplier is shown, and this calculator applies it when you give the ridge length.
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If the roof pitch calculator is not quite what you need, these other free tools solve closely related problems, and there are 17 more in home & energy calculators.
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Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.