Reference chart
Roof Pitch Chart & Calculator
Every roof pitch as an angle, a grade and the two multipliers a framer uses: the slope factor for common rafters and roof area, and the hip and valley factor. The calculator below converts any pitch, angle or measured rise and run.
Pitch to degrees, percent and slope factor
| Pitch | Degrees | Percent | Slope factorcommon rafter / roof area | Hip / valley | Where you see it |
|---|---|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.0035 | 1.4167 | Flat / low-slope (membrane roofing only) |
| 2:12 | 9.46° | 16.7% | 1.0138 | 1.4240 | Low slope (minimum for asphalt shingles is 2:12 with special underlayment; 4:12 standard) |
| 3:12 | 14.04° | 25% | 1.0308 | 1.4361 | Low slope (minimum for asphalt shingles is 2:12 with special underlayment; 4:12 standard) |
| 4:12 | 18.43° | 33.3% | 1.0541 | 1.4530 | Conventional, walkable |
| 5:12 | 22.62° | 41.7% | 1.0833 | 1.4743 | Conventional, walkable |
| 6:12 | 26.57° | 50% | 1.1180 | 1.5000 | Conventional, walkable |
| 7:12 | 30.26° | 58.3% | 1.1577 | 1.5298 | Conventional, walkable |
| 8:12 | 33.69° | 66.7% | 1.2019 | 1.5635 | Conventional, walkable |
| 9:12 | 36.87° | 75% | 1.2500 | 1.6008 | Conventional, walkable |
| 10:12 | 39.81° | 83.3% | 1.3017 | 1.6415 | Steep; roof jacks or staging to work on |
| 11:12 | 42.51° | 91.7% | 1.3566 | 1.6853 | Steep; roof jacks or staging to work on |
| 12:12 | 45.00° | 100% | 1.4142 | 1.7321 | Steep; roof jacks or staging to work on |
| 14:12 | 49.40° | 116.7% | 1.5366 | 1.8333 | Very steep; requires full staging |
| 16:12 | 53.13° | 133.3% | 1.6667 | 1.9437 | Very steep; requires full staging |
| 18:12 | 56.31° | 150% | 1.8028 | 2.0616 | Very steep; requires full staging |
| 24:12 | 63.43° | 200% | 2.2361 | 2.4495 | Very steep; requires full staging |
Your numbers
Pitch
6:12
Conventional, walkable
Angle
26.57°
50% grade
Slope factor
1.118
× run = common rafter length
Hip / valley factor
1.5
× run = hip rafter length
angle = atan(rise ÷ 12); factor = √(rise² + 144) ÷ 12; hip factor = √(rise² + 288) ÷ 12. Roof area = plan area × slope factor.
Questions
How do I convert roof pitch to degrees?
Angle = arctangent of rise over 12. A 6:12 roof is atan(6 ÷ 12) = 26.57°, a 4:12 is 18.43°, a 12:12 is 45°. The chart lists every pitch from 1:12 to 24:12; the calculator does any value, and the other way, degrees back to rise.
What is the slope factor and what is it for?
The ratio of rafter length to horizontal run: √(rise² + 144) ÷ 12. At 6:12 it is 1.118, so every foot of run needs 1.118 feet of rafter, and the roof surface is 1.118 times the plan area. Use it for rafter length, roofing squares and gutter-to-ridge measurements.
How do I measure the pitch of an existing roof?
Hold a level horizontally against the roof or a rafter, mark 12 inches along the level from where it touches, and measure straight down from that mark to the roof. That measurement is the rise per 12. From inside an attic, measure along the underside of a rafter the same way. Enter it in the calculator's rise-and-run mode.
What pitch do I need for shingles or metal?
Asphalt shingles need 4:12 or steeper for standard installation and are allowed down to 2:12 with doubled underlayment; below 2:12 use a membrane. Standing-seam metal goes to 3:12, some profiles to ½:12. Tile and slate want 4:12 or more. Snow country favours 6:12 and up.
What about hip and valley rafters?
They run diagonally, so their run per foot of common run is √2 = 1.414 feet, and their slope factor is √(rise² + 288) ÷ 12: 1.5 at 6:12 against the common rafter's 1.118. The hip column in the chart gives the multiplier for the hip's plan length.
Charts are computed from the formulas and code figures stated on the page (International Residential Code limits where cited). They are planning and take-off numbers, not engineering: species, grade, span tables and local amendments govern anything structural. Confirm with your inspector before you cut.