6 in rise in 12 in run
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Pitch is 6:12. The angle is arctan(0.5) ≈ 26.57° and the slope is 50%. The multiplier is √1.25 ≈ 1.118, so every 12 ft of horizontal run is a 13′ 5″ rafter line.
Roof Pitch Calculator: Pitch, Degrees and Slope
Calculator
Result
A 6:12 roof rises 6 for every 12 across, a 26.57° slope. Multiply a flat run or plan area by 1.118 to get the sloped length or area.
Pitch
6:12
26.57° · 50% slope
Multiplier
1.118
Multiply the horizontal run or the plan area by this.
Rafter line
1′ 1 7/16″
For a run of 1′. Rise 6″.
Enter a plan length and width to estimate the roof surface.
Know the rise and run, the pitch, or just the angle? Type whichever you have. This roof pitch calculator, also called a roof slope calculator, converts between x:12, degrees and percent slope and gives you the multiplier and the rafter line length. One step of pitch moves a 20 ft rafter by about 9½ in, so know yours before you order lumber.
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- Reviewed 15 October 2026
- Estimates only
Quick answer A 6 in rise over a 12 in run is a 6:12 pitch: 26.57°, a 50% slope, with a rafter multiplier of 1.118. Multiply any horizontal run by it to get the rafter line length, or the plan area by it to estimate the roof surface.
How it works
Pitch is a ratio, so whatever you type becomes rise per unit of run, then comes back three ways: inches of rise per 12 inches of run, degrees, and percent. The multiplier stretches a horizontal measurement onto the slope. It goes by several names (pitch factor, roof slope factor, roof slope multiplier) but it is one number, and it is the one that turns a plan into a rafter.
How to calculate roof pitch from a rise and a run: divide the rise by the run and multiply by 12. A rise of 4 in over a run of 8 in is 4 ÷ 8 × 12 = 6, so the roof is 6:12. Any unit works as long as the rise and the run use the same one. A sloped roof is just that ratio, shown here as pitch, degrees and percent.
How to measure roof pitch from the attic: hold a level against the underside of a rafter, mark 12 in along it and measure straight up to the rafter. That distance is the x in x:12. A phone level app or a pitch gauge gives the angle directly. Either goes into this pitch calculator, and the roof slope chart below turns it into degrees and a multiplier.
A gable roof's surface is about the plan area times the multiplier, because the two slopes together cover the full plan. Overhangs are extra, so add them to the plan dimensions if you want them counted.
Once you know the pitch, the rafter length calculator turns it into a rafter length and cuts, and the roofing calculator turns it into roof square feet and shingle bundles. Check that the walls are square first with the squaring calculator.
Formula
θ = roof angle, m = rafter (pitch) multiplier.
pitch (x:12) = 12 × (rise / run) angle = arctan(rise / run) slope % = (rise / run) × 100 multiplier = √(1 + (rise / run)²) = √(144 + x²) / 12 rafter line = run × multiplier with tail = (run + horizontal overhang) × multiplier roof surface ≈ plan area × multiplier
Worked examples
4:12 over a 24 × 40 ft plan
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Known pitch 4:12 with a 12 ft run (half of a 24 ft span). The multiplier is √(1 + (4/12)²) ≈ 1.054. The 24 × 40 ft plan of 960 ft² becomes about 1011.9 ft² of roof surface before overhangs. The rafter calculator also subtracts half the ridge thickness.
A 30° UK roof in x:12
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Start from the angle. tan(30°) = 0.5774, so the pitch is 12 × 0.5774 ≈ 6.93:12 and the slope is 57.7%. The multiplier is 1.1547, so a 3 m horizontal run needs about 3.46 m of rafter line.
Roof pitch chart: pitch to degrees and multiplier
Find your pitch in the first table and read across: the angle, the percent slope and the multiplier that stretches a horizontal run onto the slope. Every row comes from the same formulas as the calculator above. The second table runs the other way, from roof angles in degrees to pitch, because that is how roofs are quoted in the UK and Europe.
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.0035 |
| 2:12 | 9.46° | 16.7% | 1.0138 |
| 3:12 | 14.04° | 25.0% | 1.0308 |
| 4:12 | 18.43° | 33.3% | 1.0541 |
| 5:12 | 22.62° | 41.7% | 1.0833 |
| 6:12 | 26.57° | 50.0% | 1.1180 |
| 7:12 | 30.26° | 58.3% | 1.1577 |
| 8:12 | 33.69° | 66.7% | 1.2019 |
| 9:12 | 36.87° | 75.0% | 1.2500 |
| 10:12 | 39.81° | 83.3% | 1.3017 |
| 11:12 | 42.51° | 91.7% | 1.3566 |
| 12:12 | 45.00° | 100.0% | 1.4142 |
| 13:12 | 47.29° | 108.3% | 1.4743 |
| 14:12 | 49.40° | 116.7% | 1.5366 |
| 15:12 | 51.34° | 125.0% | 1.6008 |
| 16:12 | 53.13° | 133.3% | 1.6667 |
| 17:12 | 54.78° | 141.7% | 1.7341 |
| 18:12 | 56.31° | 150.0% | 1.8028 |
| Angle | Pitch | Slope | Multiplier |
|---|---|---|---|
| 15.0° | 3.22:12 | 26.8% | 1.0353 |
| 20.0° | 4.37:12 | 36.4% | 1.0642 |
| 22.5° | 4.97:12 | 41.4% | 1.0824 |
| 25.0° | 5.60:12 | 46.6% | 1.1034 |
| 30.0° | 6.93:12 | 57.7% | 1.1547 |
| 35.0° | 8.40:12 | 70.0% | 1.2208 |
| 40.0° | 10.07:12 | 83.9% | 1.3054 |
| 45.0° | 12.00:12 | 100.0% | 1.4142 |
| 50.0° | 14.30:12 | 119.2% | 1.5557 |
| 55.0° | 17.14:12 | 142.8% | 1.7434 |
| 60.0° | 20.78:12 | 173.2% | 2.0000 |
Code notes
Pitch itself is geometry. What a pitch allows (asphalt shingles, wood shakes, membranes) is set by the roofing chapter of the IRC, IRC 2021 Chapter 9, Roof Assemblies, and by the product listing, and low slopes often need a different underlayment. Rafter size is a span-table question, not a pitch question. The American Wood Council publishes residential span guidance.
Outside the US, roof pitch is usually stated in degrees or as a percent. This page prints all three from the same ratio, and the chart above lists the common values in both directions.
Section numbers refer to IRC 2021 section numbers; England Approved Document K. Local amendments are common, so confirm with your building authority.
FAQ
Hover a question to read the answer. Click to keep it open.Tap a question to open it.
How do you convert roof pitch to degrees?
Pitch x:12 means the roof rises x inches for every 12 inches of run, so the angle is arctan(x ÷ 12). A 6:12 pitch is arctan(0.5), about 26.57 degrees. The chart on this page lists common pitches from 1:12 to 18:12.
How do you calculate roof pitch?
Divide the rise by the run and multiply by 12. A rise of 6 inches over a run of 12 inches is a 6:12 pitch. From the attic, hold a level against a rafter, mark 12 inches along it and measure up to the rafter. Type the numbers in and the calculator gives the pitch, the angle and the percent slope.
What are the roof pitch factor and the roof slope factor?
Both are the roof pitch multiplier: √(1 + (rise ÷ run)²), or √(144 + x²) ÷ 12. Multiply the horizontal run by it to get the rafter line length, or the plan area by it to estimate the sloped roof area. For a 6:12 roof the factor is about 1.118.
What is the difference between pitch and percent slope?
Pitch is rise per 12 inches of run. Percent slope is rise divided by run, times 100. A 6:12 pitch is a 50% slope. Degrees are the actual angle from horizontal. Much of Europe quotes roof angles in degrees, and the chart on this page converts both ways.
What pitch is a 30 degree roof?
tan(30°) is 0.5774, so a 30° roof is about 6.93:12, a 57.7% slope, with a multiplier of 1.155. The degrees-to-pitch table on this page lists other angles.
What is the minimum roof pitch for asphalt shingles?
IRC R905.2.2 allows asphalt shingles on slopes of 2:12 (about 9.5 degrees, a 17% slope) or steeper, and asks for double underlayment between 2:12 and 4:12. Metal, membrane and other coverings have their own minimums, so read the product listing before you settle on a pitch.
What is a 4/12 roof pitch, and what angle is it?
A 4:12 pitch is arctan(4 ÷ 12), about 18.43°, a 33.3% slope, with a multiplier of 1.0541. The chart on this page lists the other common pitches.
What is a 6/12 roof slope?
A 6/12 roof slope rises 6 inches for every 12 inches of horizontal run: 26.57°, a 50% slope, with a multiplier of 1.118. It is one of the most common residential pitches.