10 Minute BidsRoof pitch calculatorx/12, degrees, percent and rafters.
Enter rise and run, or a pitch, angle or percent you already have. You get the other three, the pitch factor and the rafter length.
Your estimate
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| Pitchrise in 12 in of run | — |
|---|---|
| Anglefrom level | — |
| Graderise ÷ run × 100 | — |
| Pitch factor√(1 + (rise ÷ run)²) | — |
| Rafter length | — |
| Rise over the runwall line to ridge line | — |
How we got it
Skip the math — upload your plans. We measure it all on a 3D model of your house.
Priced per plan setRoofing bid, 3D model included
Upload your plansBefore you cut: the rafter length here is the line length along the slope. Take off half the ridge board's thickness, measured level, then lay out the plumb and seat cuts.
This is an estimate from the numbers you enter. Framing that is out of level or plumb changes the real pitch. Measure on site before you cut or order materials.
The roof pitch formulas.
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Slope and pitch
Rise is how far the roof climbs, run is the level distance it covers, in the same units.
slope = rise ÷ run · pitch = 12 × slope, written x/12 -
Angle in degrees
The angle from level is the arctangent of the slope.
angle = arctan(rise ÷ run) -
Percent grade
The slope as a percent.
grade = rise ÷ run × 100 -
Pitch factor and rafter length
How much longer the roof is on the slope than across it level.
pitch factor = √(1 + slope²) · rafter = (run + overhang) × pitch factor
Worked example6 in of rise over 12 in of run is a 6/12 pitch: arctan(0.5) = 26.57°, a 50% grade and a pitch factor of 1.1180. A 12 ft run at 6/12 needs a rafter of 12 × 1.1180 = 13.42 ft, about 13 ft 5 in.
| Pitch | Angle | Grade | Factor |
|---|---|---|---|
| 1/12 | 4.76° | 8.33% | 1.0035 |
| 2/12 | 9.46° | 16.67% | 1.0138 |
| 3/12 | 14.04° | 25% | 1.0308 |
| 4/12 | 18.43° | 33.33% | 1.0541 |
| 5/12 | 22.62° | 41.67% | 1.0833 |
| 6/12 | 26.57° | 50% | 1.1180 |
| 7/12 | 30.26° | 58.33% | 1.1577 |
| 8/12 | 33.69° | 66.67% | 1.2019 |
| 9/12 | 36.87° | 75% | 1.2500 |
| 10/12 | 39.81° | 83.33% | 1.3017 |
| 11/12 | 42.51° | 91.67% | 1.3566 |
| 12/12 | 45° | 100% | 1.4142 |
| 14/12 | 49.4° | 116.67% | 1.5366 |
| 16/12 | 53.13° | 133.33% | 1.6667 |
| 18/12 | 56.31° | 150% | 1.8028 |
Skip the math —upload your plans.
Upload your plan set and we build the roof in 3D, every plane at the pitch your plans give it. Order a metal or a shingle roofing bid; you spend about 10 minutes checking it against your plans.
Priced per plan setRoofing bid, 3D model included
Or see what’s in a metal roofing bid.
Roof pitch questions.
How do I calculate roof pitch?
Measure how many inches the roof rises over 12 inches of level run. A rise of 6 over a run of 12 is a 6/12 pitch. If you measured over a different run, pitch = 12 × rise ÷ run.
How do I convert roof pitch to degrees?
Angle = arctan(rise ÷ run). A 6/12 pitch is arctan(0.5) = 26.57°. A 12/12 pitch is 45°.
What is the pitch factor?
It is how much longer the roof is along the slope than across the level run: √(1 + (rise ÷ 12)²). Multiply a level run or a plan area by it to get the slope length or the roof area. A 6/12 roof has a factor of 1.118.
How long is a rafter?
Rafter length = level run × pitch factor, overhang included. A 12 ft run at 6/12 is 12 × 1.118 = 13.42 ft, about 13 ft 5 in. Take off half the ridge board's thickness, measured level, before you cut.
Is roof pitch the same as slope?
Roofers say pitch for the rise in 12 inches of run, like 6/12, and that is what this calculator uses. Strictly, that is the slope: the old carpenter’s pitch is rise ÷ span, so a 6/12 slope is a 1/4 pitch.