Roof Pitch Calculator

US & Canada

Enter the rise and run, or the angle, to get the pitch, the slope factor for your roof area, and whether shingles are allowed.

Your roof

1. What you measured

in
in
degrees

Hold a level 12 in (or 1 m) out from the roof or rafter and measure straight down to it. Any run works; the pitch is the ratio. The angle is used only when Angle in degrees is picked.

2. Roof area (optional)

sq ft

The flat area under the roof, overhangs included. Leave at 0 to skip.

Result

0

What the pitch means

Angle, slope factor and grade are trigonometry (calculated). Shingle limits: IRC 2021 R905.2.2 and NBC 2020 Table 9.26.3.1.

How the pitch maths works

  • Pitch in 12 = rise ÷ run × 12
  • Angle = atan(rise ÷ run)
  • Slope factor = √(1 + (rise ÷ run)²), which turns footprint into roof area and run into rafter length
  • Grade = rise ÷ run × 100

These are standard trigonometry, worked out by us rather than taken from a code. Rise and run can be in any one unit, so millimetres work the same as inches.

Pitch chart

All values calculated. The last column applies to asphalt shingles.

Roof pitch to degrees, slope factor and grade
Pitch Degrees Slope factor Grade NBC style Asphalt shingles
1/12 4.76° 1.0035 8.3% 1 in 12 Not allowed
2/12 9.46° 1.0138 16.7% 1 in 6 Double underlayment (IRC); low slope (NBC)
3/12 14.04° 1.0308 25% 1 in 4 Double underlayment (IRC); low slope (NBC)
4/12 18.43° 1.0541 33.3% 1 in 3 Normal
5/12 22.62° 1.0833 41.7% 1 in 2.4 Normal
6/12 26.57° 1.118 50% 1 in 2 Normal
7/12 30.26° 1.1577 58.3% 1 in 1.71 Normal
8/12 33.69° 1.2019 66.7% 1 in 1.5 Normal
9/12 36.87° 1.25 75% 1 in 1.33 Normal
10/12 39.81° 1.3017 83.3% 1 in 1.2 Normal
11/12 42.51° 1.3566 91.7% 1 in 1.09 Normal
12/12 45° 1.4142 100% 1 in 1 Normal
14/12 49.4° 1.5366 116.7% 1 in 0.86 Normal
16/12 53.13° 1.6667 133.3% 1 in 0.75 Normal
18/12 56.31° 1.8028 150% 1 in 0.67 Normal
24/12 63.43° 2.2361 200% 1 in 0.5 Normal

Shingle minimums: US and Canada

  • US, IRC 2021 R905.2.2: "Asphalt shingles shall be used only on roof slopes of 2 units vertical in 12 units horizontal (17-percent slope) or greater." From 2:12 up to 4:12, double underlayment is required (Section R905.1.1).
  • Canada, NBC 2020 Table 9.26.3.1: asphalt shingles, low slope application 1 in 6, normal application 1 in 3. Below 1 in 3, Subsection 9.26.8 applies; for example, coverage must be at least 3 thicknesses of shingle except for the first 2 courses (9.26.8.1).
  • Ontario: the Ontario amendments to the NBC 2020 replace Table 9.26.3.1, but print the same asphalt shingle values (1 in 6 and 1 in 3).

Shingle makers can set their own minimums; follow the wrapper on the bundle if it is stricter.

Sources

Angles, slope factors, grades and the 1 in 6 = 2:12 and 1 in 3 = 4:12 equivalents are calculated.

Common questions

What angle is a 6/12 roof pitch?
26.57°. The angle is atan(6 ÷ 12). Its slope factor is 1.118, so a 6/12 roof has about 11.8% more surface than its footprint.
What is the minimum pitch for asphalt shingles?
2 in 12 in the US: IRC 2021 R905.2.2 allows asphalt shingles only on slopes of 2:12 (17 percent) or more, with double underlayment from 2:12 up to 4:12. In Canada, NBC 2020 Table 9.26.3.1 sets 1 in 6 for low slope application and 1 in 3 for normal application. 1 in 6 equals 2:12 and 1 in 3 equals 4:12 (calculated).
What is 4/12 pitch in degrees?
18.43°, a 33.3% grade, slope factor 1.0541. It is where normal shingle application starts under both codes.
How do I convert degrees to pitch?
Pitch in 12 = tan(angle) × 12. A 30° roof is 6.93 in 12. Pick Angle in degrees in the calculator to do it for any angle.
How do I measure roof pitch?
Put a level against a rafter or the roof surface, mark 12 in along it, and measure straight down (or up) to the roof. That distance in inches is the pitch in 12. In metric, use a 1 m run: the rise in millimetres divided by 1,000, times 12, gives the pitch in 12.
How much roof area is on a 1,500 sq ft footprint at 6/12?
Footprint × slope factor: 1,500 × 1.118 = 1,677 sq ft (155.8 m²) of roof, before waste. The roofing calculator turns that into bundles.
What does 1 in 3 mean on a Canadian roof?
One unit of rise for every 3 of run, the way the NBC writes slope. It is the same as 4 in 12, about 18.4°.