Roof Pitch Calculator
Enter a pitch, an angle, or a rise and run to get the pitch every way it is written. Add the building width and footprint for rafter length and roof area.
- Angle
- 26.57°
- Percent slope
- 50%
- Ratio
- 1 : 2
- Pitch multiplier
- 1.118
- Pitch (rise ÷ span)
- 1/4
- Ridge height
- 6 ft
- Rafter length
- 13.42 ft
- With overhang
- 14.53 ft
- Roof area
- 1,677 sq ft · 16.8 squares
Can this pitch take the covering?
Minimum slopes from the 2021 International Residential Code, section R905. Your local code and the manufacturer's instructions may be stricter.
| Covering | Minimum | This roof |
|---|---|---|
| Asphalt shinglesFrom 2/12 up to 4/12, double underlayment is required (R905.2.2). | 2/12 | ✓ Allowed |
| Clay or concrete tileR905.3.2 | 2.5/12 | ✓ Allowed |
| Metal roof shinglesR905.4.2 | 3/12 | ✓ Allowed |
| Wood shinglesR905.7.2 | 3/12 | ✓ Allowed |
| Wood shakesR905.8.2 | 3/12 | ✓ Allowed |
| Slate shinglesR905.6.2 | 4/12 | ✓ Allowed |
| Metal panels, lapped seams, no sealantR905.10.2 | 3/12 | ✓ Allowed |
| Metal panels, lapped seams with sealantR905.10.2 | 0.5/12 | ✓ Allowed |
| Metal panels, standing seamR905.10.2 | 0.25/12 | ✓ Allowed |
Roof pitch chart
| Pitch | Angle | Percent | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 |
| 2/12 | 9.46° | 16.7% | 1.014 |
| 3/12 | 14.04° | 25% | 1.031 |
| 4/12 | 18.43° | 33.3% | 1.054 |
| 5/12 | 22.62° | 41.7% | 1.083 |
| 6/12 | 26.57° | 50% | 1.118 |
| 7/12 | 30.26° | 58.3% | 1.158 |
| 8/12 | 33.69° | 66.7% | 1.202 |
| 9/12 | 36.87° | 75% | 1.25 |
| 10/12 | 39.81° | 83.3% | 1.302 |
| 11/12 | 42.51° | 91.7% | 1.357 |
| 12/12 | 45° | 100% | 1.414 |
Sloping a ramp, path or driveway instead? Use the slope percentage calculator, which checks ADA ramp limits.
How roof pitch works
Roof pitch in the US is written as the rise in inches for every 12 inches of horizontal run. A 4/12 roof climbs 4 inches per foot; a 12/12 roof climbs a foot per foot, which is 45°. Because it is a ratio, any unit works, as long as the rise and run use the same one.
The same slope can be written as an angle (the arctangent of rise ÷ run), apercent (rise ÷ run × 100, the way roads and ramps are described) or aratio such as 1:2. Strictly, carpenters reserve the word pitch for rise divided by the full span of a gable, so a 6/12 slope is a "quarter pitch". Most people, and most roofing products, use pitch to mean the x/12 figure.
The pitch multiplier converts flat measurements to sloped ones. A rafter is its run times the multiplier, and the roof surface is its footprint times the multiplier, which is how roofers estimate shingles from a plan. Roofing is sold in squares of 100 sq ft. Add a waste allowance on top for cuts, ridges, hips and valleys; the manufacturer or supplier can tell you how much for your roof shape.
Pitch also decides which coverings are allowed. Shingles rely on water running off, so the code sets a minimum slope for each material. Below about 2/12, only systems sealed against standing water, such as membrane roofs or standing-seam metal, are suitable.
Frequently asked questions
How do you calculate roof pitch?
Measure the rise (how far the roof climbs) over a known horizontal run, then scale it to a 12-inch run: pitch = rise ÷ run × 12. A roof that rises 9 inches over 18 inches of run is 9 ÷ 18 × 12 = 6, so a 6/12 pitch. On site, hold a level 12 inches long against the roof and measure straight down from its end to the roof surface; that number is the pitch.
How do I convert roof pitch to degrees?
Take the arctangent of the rise divided by the run: degrees = arctan(pitch ÷ 12). A 6/12 roof is arctan(0.5) = 26.57°, a 4/12 roof is 18.43°, and a 12/12 roof is exactly 45°. The table on this page lists 1/12 to 12/12.
What is the difference between roof pitch and roof slope?
In everyday use they mean the same thing, written as inches of rise per 12 inches of run, such as 6/12 or 6:12. Strictly, carpenters define pitch as the rise divided by the whole span of a gable, which is twice the run, so a 6/12 slope is a 1/4 pitch and a 12/12 slope a 1/2 pitch. This calculator shows both.
How do I calculate rafter length?
For a symmetrical gable, the run is half the building span. The rafter length along the slope is run × √(1 + (pitch ÷ 12)²). A 24-foot span at 6/12 has a 12-foot run and a rafter of 12 × 1.118 = 13.42 feet. An overhang measured level is multiplied the same way. This is the length along the rafter's line; ridge-board and birdsmouth cuts are adjusted for on the actual framing.
What is the pitch multiplier and how do I use it for roof area?
The pitch multiplier, √(1 + (pitch ÷ 12)²), is how much longer a sloped surface is than the flat ground it covers. Multiply the roof's footprint, including the overhangs, by it to get the sloped roof area. A 1,500 sq ft footprint at 6/12 has about 1,677 sq ft of roof, or 16.8 squares (a roofing square is 100 sq ft). Order extra for waste, ridges and valleys.
What is the minimum roof pitch for shingles?
The 2021 International Residential Code allows asphalt shingles on roofs of 2/12 or steeper, and requires double underlayment from 2/12 up to 4/12 (section R905.2.2). Slate needs at least 4/12, wood shingles and shakes and metal roof shingles 3/12, and clay or concrete tile 2½/12. Your local code and the manufacturer's instructions can be stricter, so check both.