Roof Pitch Calculator
Enter any one of rise and run, an x-in-12 pitch, an angle, or a percent grade, and get the rest at once, plus the slope multiplier that turns a flat footprint into true roof area. It is free to use and needs no signup.
Rise and run in the same units. Keep run at 12 to read the pitch as rise-in-12.
The horizontal run from eave to ridge. Enter it to also get the rafter length.
Drawn to your pitch
Drawn to your pitch
Roof pitch
6:12
Conventional slope
Standard slope for asphalt shingles, metal, tile, or slate. Generally walkable with normal care.
You have the pitch. Now put it on the real roof.
That is the slope for one plane. In Easy Takeoffs you measure every roof plane off the plan PDF to scale and apply this pitch as the slope factor, so your true roof area and squares come off the drawing, not a tape on the ridge. 14-day trial, no card.
What are the common roof pitches?
The slope multiplier is the number that turns a flat footprint into true roof area: multiply the footprint by it and you get the surface you actually cover. A 6:12 roof has a multiplier of 1.118, so a 2,000 square foot footprint is about 2,236 square feet of roof, and the steeper the pitch the larger the multiplier. Every common pitch, with its angle, percent grade, and multiplier, is charted below.
Common roof pitches
| Pitch | Angle | Percent grade | Slope multiplier |
|---|---|---|---|
| 1:12 | 4.76° | 8.33% | 1.0035 |
| 2:12 | 9.46° | 16.67% | 1.0138 |
| 3:12 | 14.04° | 25.00% | 1.0308 |
| 4:12 | 18.43° | 33.33% | 1.0541 |
| 5:12 | 22.62° | 41.67% | 1.0833 |
| 6:12 | 26.57° | 50.00% | 1.1180 |
| 7:12 | 30.26° | 58.33% | 1.1577 |
| 8:12 | 33.69° | 66.67% | 1.2019 |
| 9:12 | 36.87° | 75.00% | 1.2500 |
| 10:12 | 39.81° | 83.33% | 1.3017 |
| 11:12 | 42.51° | 91.67% | 1.3566 |
| 12:12 | 45.00° | 100.00% | 1.4142 |
Angle to two decimals, multiplier to four. Two pitches are exact fractions: 5:12 (a 5-12-13 triangle) is 13/12 = 1.0833, and 9:12 is 15/12 = 1.2500.
How do you measure a roof pitch?
You measure a roof pitch as the rise over 12 inches of level run. All you need is a level and a tape measure, and you can do it on the roof, at the eave, or from inside the attic.
- 1
Rest a level against the roof surface or a rafter and hold it perfectly level.
- 2
Measure 12 inches along the level from the end that touches the roof, and mark it.
- 3
From that 12-inch mark, measure straight down to the roof. That vertical distance in inches is the rise.
- 4
The pitch is that rise over 12: a 6-inch rise is a 6:12 pitch. Enter it above for the angle, percent, and slope multiplier.
What roof pitch should you use?
Most homes use a 4:12 to 9:12 pitch, and 6:12 is the most common. Steeper pitches shed snow and rain faster, last longer, and give more attic space; lower pitches use less material and are easier to work on but limit your covering options. Climate and roof style set the right pitch as much as looks do.
Recommended pitch by situation
| Situation | Typical pitch |
|---|---|
| Standard residential | 4:12 to 9:12 (6:12 most common) |
| Heavy snow | 6:12 or steeper, to shed snow |
| High wind | 4:12 to 6:12, a lower profile |
| Modern or low-slope look | 2:12 to 4:12 (check the covering limits) |
| Porch or shed roof | 3:12 to 4:12 |
| Steep or architectural accent | 10:12 to 12:12 and up |
General guidance. Local code, snow load, and wind zone set the real minimums, so confirm with your building department.
How do you calculate roof pitch?
Roof pitch is the ratio of vertical rise to horizontal run, written as x-in-12. Every other form comes from that one ratio: the angle is its arctangent, the percent grade is the ratio times 100, and the slope multiplier is the square root of one plus the ratio squared. Here is the exact math, with a worked example.
- Pitch (x:12)
- rise ÷ run × 12
- Angle (degrees)
- the arctangent of rise ÷ run
- Percent grade
- rise ÷ run × 100
- Slope multiplier
- √(1 + (rise ÷ run)²), which for an x:12 pitch is √(x² + 144) ÷ 12
- Rafter length
- the horizontal run length × the slope multiplier
Worked example
A roof that rises 6 inches for every 12 inches of run
- Ratio: 6 ÷ 12 = 0.5
- Pitch: 0.5 × 12 = 6, so 6:12
- Angle: the arctangent of 0.5 = 26.57°
- Percent grade: 0.5 × 100 = 50%
- Slope multiplier: √(1 + 0.5²) = √1.25 = 1.118
Roof Pitch reference tables
Minimum roof pitch by material
| Roofing material | Minimum pitch |
|---|---|
| Asphalt shingles | 2:12 (double underlayment below 4:12) |
| Standing-seam metal (sealed) | About 1:12, per panel profile |
| Exposed-fastener metal | 3:12 |
| Clay or concrete tile | 2.5:12 with underlayment, else 4:12 |
| Slate | 4:12 |
| Low-slope membrane (TPO, EPDM, built-up) | About 0.25:12 (2%) |
Code minimums from IRC R905; always follow the manufacturer spec for the warranty. These are minimums, not recommendations.
Slope categories and walkability
| Pitch | Category | Walking on it |
|---|---|---|
| Under 2:12 | Flat or near-flat | Walkable |
| 2:12 to under 4:12 | Low-slope | Walkable |
| 4:12 to 9:12 | Conventional | Walkable to about 6:12, then caution |
| 10:12 and steeper | Steep | Roof jacks or a harness |
Category is typical practice. Walkability is a trade rule of thumb, not code; building code treats anything under 3:12 as a safe working surface.
Roof Pitch Calculator Questions
Roof pitch is how steep a roof is, written as the vertical rise over 12 inches of horizontal run, such as 6:12. The same steepness can be written three ways: the x-in-12 ratio, an angle in degrees, or a percent grade. A 6:12 roof rises 6 inches per foot of run, which is a 26.57 degree angle and a 50 percent grade.
A 4:12 pitch rises 4 inches for every 12 inches of horizontal run. That is an 18.43 degree angle, a 33.3 percent grade, and a slope multiplier of 1.054. It is the lowest pitch most asphalt shingles are rated for with a single underlayment, and the low end of the common residential range.
As a rule of thumb, most roofers walk a pitch up to about 6:12 with normal care, use caution around 7:12, and set up roof jacks, brackets, or a harness at 8:12 and steeper. This is trade guidance, not code. Building code treats anything under 3:12 as a safe low-slope working surface.
Most residential roofs fall between 4:12 and 9:12, and 6:12 is the most common. Below 4:12 is low-slope, which limits your covering options. 10:12 and steeper is a steep roof that needs staging to work on safely.
In snowy climates use 6:12 or steeper so snow slides off instead of building up. A steeper pitch cuts the snow load and helps prevent ice dams, so many cold-climate homes settle between 6:12 and 9:12. Below 4:12 snow lingers, and the roof needs a stronger structure and careful waterproofing.
The slope multiplier, or slope factor, converts a flat footprint into the true sloped area. Measure the roof footprint, then multiply by the factor for its pitch. A 6:12 roof has a multiplier of 1.118, so a 2,000 square foot footprint is about 2,236 square feet of actual roof, which is the area you order material for.
Take the arctangent of the rise over the run. For an x:12 pitch that is the arctangent of x divided by 12. So 4:12 is 18.43 degrees, 6:12 is 26.57 degrees, 9:12 is 36.87 degrees, and 12:12 is exactly 45 degrees. The chart above lists every common pitch.
Asphalt shingles can go down to 2:12, but from 2:12 up to 4:12 they require a double layer of underlayment. At 4:12 and steeper a single underlayment is allowed. Below 2:12 shingles are not rated and the warranty is void, so a low-slope membrane is used instead. This is set by IRC R905.
It depends on the panel. Sealed, mechanically seamed standing-seam panels can go as low as about 1:12, and some to a quarter-in-12. Exposed-fastener and lapped panels without seam sealant need at least 3:12. Always follow the manufacturer spec for the warranty.
Between 2:12 and 4:12 you can shingle if you install a double underlayment, per code. Below 2:12 asphalt shingles are not permitted, so a low-slope membrane such as TPO, EPDM, or built-up roofing is used instead, which works down to about a quarter-in-12.
Measure it in the attic. Hold a level against the underside of a rafter, mark 12 inches along it, and measure straight down to the rafter. The rise over 12 is your pitch. This is the safest method and needs only a level and a tape measure.
Yes. It is free, needs no signup, and runs entirely in your browser. Nothing you enter is uploaded anywhere.
No. This calculator converts a pitch you already know. To pull roof planes and their slopes off a PDF plan to scale and take off the true roof area, use Easy Takeoffs, the construction takeoff software built to measure off plans. 14-day trial, no card.
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