Roof Pitch Calculator: What's the Pitch of My Roof?
Enter what you measured and get the pitch, angle, slope and area multiplier instantly, plus which roofing materials the code allows at that pitch.
Roof pitch is how many inches the roof rises for every 12 inches it runs horizontally. A roof that climbs 6 inches over 12 inches of level distance is a 6/12 pitch, said “six in twelve.” Roofers, inspectors and material manufacturers all use this format, so it’s the number you’ll want when you talk to a contractor or read a shingle wrapper.
How it works
The calculator turns any of three inputs into the same set of results. With rise and run, the math is a ratio scaled to a 12-inch run:
pitch (x/12) = 12 × rise ÷ run
angle (degrees) = arctan(rise ÷ run)
slope (%) = 100 × rise ÷ run
pitch multiplier = √(1 + (rise ÷ run)²)Rise is the vertical distance and run is the level, horizontal distance. They only need to be in the same unit, so 3 inches over 6 inches gives the same answer as 6 over 12. If you start from an angle, the calculator works backward with the tangent: pitch = 12 × tan(angle).
The pitch multiplier is the number most people actually need. It’s the length of the sloped surface for every foot of horizontal run, which also makes it the ratio between the roof’s true area and its footprint. Multiply the footprint (including overhangs) by the multiplier and you have the area you’ll be buying materials for.
If you enter the horizontal run of the rafter, usually half the building’s width on a simple gable, you also get the rafter length from the wall to the ridge and the total height the roof gains. That length doesn’t include the overhang or the ridge board thickness, so add those before you cut anything.
Assumptions: the roof plane is flat and true, and your run measurement is level. The material list uses the minimum slopes in the 2021 International Residential Code, Section R905. Your local code or the manufacturer’s instructions may be stricter, and they win.
Worked example
Say you’re in the attic of a 28-foot-wide gable house. You hold a 2-foot level against the bottom edge of a rafter, mark 12 inches from the end that touches the rafter, and measure straight up from that mark to the rafter: 7 inches.
- Pitch: 12 × 7 ÷ 12 = 7/12
- Angle: arctan(7 ÷ 12) = 30.26°
- Multiplier: √(1 + 0.583²) = 1.158
- Rafter run is half the width, 14 ft, so the roof rises 14 × 7 ÷ 12 = 8.17 ft (about 8 ft 2 in) to the ridge
- Rafter length, wall to ridge: 14 × 1.158 = 16.21 ft (about 16 ft 2½ in), before the overhang
Now the area. The house is 28 × 40 ft, with a 1-foot overhang on every side, so the footprint under the roof is 30 × 42 = 1,260 sq ft. Multiply by 1.158 and the sloped roof area is about 1,459 sq ft, or roughly 14.6 roofing squares before waste.
Roof pitch reference table
| Pitch | Angle | Slope | Multiplier | Type |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | Low-slope roof |
| 2/12 | 9.46° | 16.7% | 1.014 | Low-slope roof |
| 3/12 | 14.04° | 25.0% | 1.031 | Low-slope roof |
| 4/12 | 18.43° | 33.3% | 1.054 | Conventional pitch |
| 5/12 | 22.62° | 41.7% | 1.083 | Conventional pitch |
| 6/12 | 26.57° | 50.0% | 1.118 | Conventional pitch |
| 7/12 | 30.26° | 58.3% | 1.158 | Conventional pitch |
| 8/12 | 33.69° | 66.7% | 1.202 | Conventional pitch |
| 9/12 | 36.87° | 75.0% | 1.250 | Conventional pitch |
| 10/12 | 39.81° | 83.3% | 1.302 | Steep roof |
| 11/12 | 42.51° | 91.7% | 1.357 | Steep roof |
| 12/12 | 45.00° | 100.0% | 1.414 | Steep roof |
| 13/12 | 47.29° | 108.3% | 1.474 | Steep roof |
| 14/12 | 49.40° | 116.7% | 1.537 | Steep roof |
| 15/12 | 51.34° | 125.0% | 1.601 | Steep roof |
| 16/12 | 53.13° | 133.3% | 1.667 | Steep roof |
| 17/12 | 54.78° | 141.7% | 1.734 | Steep roof |
| 18/12 | 56.31° | 150.0% | 1.803 | Steep roof |
Tips and common mistakes
Measure level, not along the roof. The most common error is laying the tape on the roof surface and measuring 12 inches along the slope. On a 6/12 roof that gives you a rise of about 5⅜ inches instead of 6, so the pitch comes out low. Keep the level’s bubble centered and measure the run horizontally.
Take more than one reading. Older roofs sag between rafters, and a single spot can be off by half an inch. Measure two or three rafters and use the typical value. If the readings differ by more than an inch, the framing may have a problem worth having a roofer look at.
Watch for “pitch” meaning something else. In older carpentry books, pitch is rise divided by the full span, so a “1/3 pitch” roof is 8/12 and a “1/4 pitch” roof is 6/12. Modern roofing always means rise per 12 inches of run. If a document gives a fraction without the “/12,” check which one it means.
Low-slope roofs need the right system. Asphalt shingles are allowed down to 2/12, but between 2/12 and 4/12 the code requires double underlayment, and many roofers prefer a membrane or standing-seam metal below 3/12. Tile has a code minimum of 2½/12, and some tile makers want 4/12 for their standard installation.
Pitch changes the price. Steeper roofs need more material per square foot of footprint, and above about 7/12 most crews charge more for labor and safety setup. A 12/12 roof has 41% more surface than a flat roof over the same footprint.
Stay off steep roofs. You don’t need to climb up to get a good number. The attic method is accurate, and a phone angle reading from the gable end is close enough for planning. If you do go up, use fall protection; falls are one of the leading causes of death in construction.
Frequently asked questions
What is a normal roof pitch for a house?
Most US houses fall between 4/12 and 9/12, and 6/12 is one of the most common. Ranch homes in the South and West often sit at 4/12 or 5/12, while snowy regions and steep styles like Tudor or Victorian go well above 9/12.
How can I find my roof pitch without getting on the roof?
Go into the attic and hold a level against the underside of a rafter. Mark 12 inches along the level and measure straight up to the rafter. You can also stand back from a gable end and read the roof angle with a phone inclinometer app, then switch the calculator to degrees.
What is the minimum pitch for asphalt shingles?
The 2021 IRC allows asphalt shingles down to 2/12. Between 2/12 and 4/12 the code requires two layers of underlayment. Below 2/12 you need a low-slope system such as a membrane or standing-seam metal.
What roof pitch is too steep to walk on?
Many roofers walk 6/12 comfortably and start using roof jacks or harnesses around 7/12 or 8/12. OSHA defines a steep roof as anything over 4/12 for construction work. If you are not trained and equipped for fall protection, stay off the roof and measure from the attic or the ground.
How do I convert roof pitch to degrees?
Divide the rise by 12 and take the arctangent. A 6/12 roof is arctan(0.5), which is 26.57 degrees. To go the other way, take the tangent of the angle and multiply by 12, so 30 degrees is about 6.93/12.
Does a steeper roof cost more to replace?
Yes, in two ways. A steeper roof has more surface area over the same footprint, so it needs more material, and roofers usually add a steep-slope labor charge above about 7/12 or 8/12 because the work is slower and needs more safety gear.