What does a roof pitch like 6/12 mean?

It means the roof rises 6 units for every 12 units of horizontal run. The second number is almost always 12 in US framing, so 6/12 reads as six in twelve. A 6/12 pitch works out to about 26.57 degrees and a 50 percent slope. The notation is handy on site because a framing square is marked in twelfths, so you can lay out 6 and 12 directly without doing any trig.

How do I convert a roof pitch to an angle in degrees?

Take the arctangent of rise divided by run. For 6/12 that is arctan(6 ÷ 12) = arctan(0.5) ≈ 26.57 degrees. A 4/12 roof is about 18.43 degrees and a 12/12 roof is exactly 45 degrees. This tool does it for you the moment you type the pitch, and it also runs the conversion backwards if you only know the angle.

Why is a 4/12 roof about 18.4 degrees?

Because arctan(4 ÷ 12) = arctan(0.333) is roughly 18.43 degrees. The 4/12 pitch is a common low-slope shingle roof, right at the edge of where many shingle products need a double underlayment. Knowing it sits near 18 degrees helps when a product spec quotes a minimum angle rather than a rise over run.

What is the difference between pitch percent and pitch in degrees?

Percent slope is rise divided by run times 100, so 6/12 is 50 percent. Degrees is the angle the roof line makes with horizontal, so 6/12 is about 26.57 degrees. They are not the same scale: a 100 percent slope is 45 degrees, not 90. Building codes and drainage specs often use percent, while framing crews think in rise over run and architects in degrees.

How does the rafter multiplier give me rafter length?

The rafter multiplier is √(rise² + run²) ÷ run, the length of the sloped line per unit of horizontal run. For 6/12 it is about 1.118, so a rafter spanning a 4 metre horizontal run is 4 × 1.118 ≈ 4.47 metres before any overhang. Multiply your horizontal run by the multiplier and you have the line length to cut. The tool shows the multiplier and, if you enter the run length, the finished rafter length.

What run length should I enter for a gable roof?

For a simple symmetric gable, enter half the building span, because each rafter only covers from the ridge to the wall, which is half the total width. If a house is 8 metres wide, the run is 4 metres and the tool returns the rafter length for one side. Add your eave overhang separately; this figure is the structural line length from ridge to the outside wall.

Translate a 6/12 spec into the angle your saw wants

The plans say a 6/12 main roof but your miter saw and rafter layout think in degrees. Type 6 over 12 and read 26.57 degrees straight off. Set the saw, cut the test rafter, and check it against the SVG cross-section before you commit a whole bundle of framing lumber.

Buy the right amount of rafter stock for a gable

You know the building is 8 metres wide and the roof is 8/12. Enter the pitch, set the run to 4 metres (half the span), and the tool returns the rafter line length. Multiply by the number of rafters, add your overhang and waste, and the lumber order stops being a guess.

Check a low-slope roof against a shingle minimum

A shingle product sheet lists a minimum slope in percent, not in rise over run. Punch in your 3/12 and read 25 percent, or about 14 degrees, then compare it to the spec. If you are below the single- layer threshold you find out now, not after the underlayment is down.

Match an architect's degree drawing to a framer's notation

The architect dimensioned the roof at 22.5 degrees but the framing crew needs an x/12 number to lay out with a framing square. Switch to angle mode, type 22.5, and the tool hands back roughly a 5/12 pitch so both trades are working from the same slope.

Roof Pitch Calculator — Rise Over Run, Degrees, Percent

Convert roof pitch between rise-over-run, degrees and percent, plus the rafter multiplier and real rafter length — browser-only

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Roofers write a slope as rise-over-run (6/12), architects want it in degrees, and the building code often quotes a percentage. This converter ties all three together and adds the rafter multiplier — the number you multiply the horizontal run by to get the real sloped length before you cut any lumber.

I know the

RiseRun

Horizontal run (optional)Length unit

Half the building span for a simple gable. Leave blank to skip the rafter length.

Cross-section

Pitch (x/12)

6/12

Angle

26.57°

Slope

50%

Rafter multiplier

1.118

multiply the run by this for the sloped length

What this tool does

Free roof pitch calculator that converts a roof slope between the three ways people actually write it: rise over run (the 6/12 framing notation), angle in degrees, and slope as a percentage. Type any one of them and the other two update instantly, alongside the rafter multiplier — the factor you multiply a horizontal run by to get the true sloped length before you cut any lumber. Give it the horizontal run (half the building span for a simple gable) and it returns the actual rafter length in metres or feet. A scaled cross-section keeps the geometry honest so a 4/12 really does read as about 18.4 degrees. Everything runs in your browser, with one-click copy and a shareable URL that reproduces the exact roof you set up. 100% client-side, nothing uploaded.

Tool details

Input: Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy + Preview; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 10 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Operations; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Roof Pitch Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Translate a 6/12 spec into the angle your saw wants
The plans say a 6/12 main roof but your miter saw and rafter layout think in degrees. Type 6 over 12 and read 26.57 degrees straight off. Set the saw, cut the test rafter, and check it against the SVG cross-section before you commit a whole bundle of framing lumber.
Buy the right amount of rafter stock for a gable
You know the building is 8 metres wide and the roof is 8/12. Enter the pitch, set the run to 4 metres (half the span), and the tool returns the rafter line length. Multiply by the number of rafters, add your overhang and waste, and the lumber order stops being a guess.
Check a low-slope roof against a shingle minimum
A shingle product sheet lists a minimum slope in percent, not in rise over run. Punch in your 3/12 and read 25 percent, or about 14 degrees, then compare it to the spec. If you are below the single- layer threshold you find out now, not after the underlayment is down.
Match an architect's degree drawing to a framer's notation
The architect dimensioned the roof at 22.5 degrees but the framing crew needs an x/12 number to lay out with a framing square. Switch to angle mode, type 22.5, and the tool hands back roughly a 5/12 pitch so both trades are working from the same slope.

Common pitfalls

Confusing percent slope with degrees. A 50 percent slope is 6/12 and about 26.57 degrees, not 50 degrees. Percent is rise over run times 100, while degrees is the actual angle, and a 100 percent slope tops out at 45 degrees. Always confirm which scale a spec is quoting before you set a saw.
Multiplying the full building span by the rafter multiplier. For a gable, each rafter only spans from ridge to wall, which is HALF the width. Feeding the whole 8 metre span instead of 4 metres doubles every rafter and blows the lumber order. Enter half the span as the run length.
Forgetting the rafter multiplier and using the horizontal run as the rafter length. A 6/12 rafter is about 11.8 percent longer than its horizontal projection. Cutting rafters to the flat run leaves every piece short, so always multiply the run by √(rise² + run²) ÷ run first.

Privacy

Every conversion — pitch to angle, angle to pitch, the percentage, the rafter multiplier and the rafter length — is plain JavaScript that runs in your browser tab. No roof dimension or measurement ever leaves the page, and nothing is logged. The one caveat: the shareable URL encodes your slope and run length in the query string, so a share link pasted into chat records those numbers in the recipient server's access log. For a confidential job, use the copy button and paste the text instead.

FAQ

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Roof Pitch Calculator — Rise Over Run, Degrees, Percent

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Roof Pitch Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Translate a 6/12 spec into the angle your saw wants

Buy the right amount of rafter stock for a gable

Check a low-slope roof against a shingle minimum

Match an architect's degree drawing to a framer's notation

Common pitfalls

Privacy

FAQ

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