x/12 pitch
Roof pitch and slope calculator.
Convert roof pitch to degrees and percent, and get the rafter length and area factor for your span — in the x/12 notation roofers actually use.
Enter just the rise. A 6/12 pitch means typing 6.
Half the span for a symmetrical gable. Units welcome: 12 ft, 3.6 m.
Common Pitches
Angle
26.57°
Percent Grade
50%
Rafter Length
13′ 5″
Total Rise
6′
Roof Area Factor
1.118
Category
Conventional
The standard range for shingles, tile and metal. Walkable for most roofers without staging.
Pitch Reference
| Pitch | Angle | Grade | Area Factor | Category |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.0035 | Low slope |
| 2/12 | 9.46° | 16.7% | 1.0138 | Low slope |
| 3/12 | 14.04° | 25.0% | 1.0308 | Conventional |
| 4/12 | 18.43° | 33.3% | 1.0541 | Conventional |
| 5/12 | 22.62° | 41.7% | 1.0833 | Conventional |
| 6/12 | 26.57° | 50.0% | 1.1180 | Conventional |
| 7/12 | 30.26° | 58.3% | 1.1577 | Conventional |
| 8/12 | 33.69° | 66.7% | 1.2019 | Conventional |
| 9/12 | 36.87° | 75.0% | 1.2500 | Conventional |
| 10/12 | 39.81° | 83.3% | 1.3017 | Steep slope |
| 12/12 | 45.00° | 100.0% | 1.4142 | Steep slope |
| 14/12 | 49.40° | 116.7% | 1.5366 | Steep slope |
| 16/12 | 53.13° | 133.3% | 1.6667 | Steep slope |
| 18/12 | 56.31° | 150.0% | 1.8028 | Steep slope |
| 24/12 | 63.43° | 200.0% | 2.2361 | Steep slope |
Reading the x/12 Notation
Roofers describe roof slope as rise per twelve units of run. A 6/12 pitch climbs six inches for every foot travelled horizontally. The twelve never changes, which is why a pitch is usually spoken as a single number — "a six twelve" — with the denominator taken as read.
The run is the horizontal distance from the outside of the wall to the point below the ridge, which on a symmetrical gable roof is half the span. Measuring the full span instead is the most common way to end up with a rafter cut twice as long as it should be.
Rafter Length
The rafter is the hypotenuse of a right triangle whose base is the run and whose height is the rise, so its length is:
rafter = run × √(1 + (pitch ÷ 12)²)
That square root is also the roof area factor: multiply the building's footprint by it to get the true surface area of the roof, which is what you order materials against. A 6/12 roof has a factor of about 1.118, so a 2,000 sq ft footprint carries roughly 2,236 sq ft of roof.
The number this calculator gives you is the theoretical line length. Before cutting, allow for the overhang you want, subtract half the ridge board thickness, and account for the plumb cut and birdsmouth. Those adjustments depend on your framing details, so they are deliberately left out here rather than guessed at.
What the Roof Slope Decides
- Below 2/12 — a low-slope roof. Shingles are generally not rated for it; membrane systems are used instead.
- 2/12 to 4/12 — shingles are usually permitted with a doubled underlayment. Check the manufacturer's instructions, because this is where most warranty disputes start.
- 4/12 to 9/12 — the conventional range. Walkable, sheds water well, compatible with nearly every covering.
- Above 9/12 — steep-slope work. Roof jacks or staging become necessary, labour costs rise, and the roof surface area grows quickly relative to the footprint.
To convert a pitch into the units used elsewhere on a drawing, the slope to degrees converter handles percent, degrees and ratio in one place.
Common Questions
What does a 6/12 roof pitch mean?
A 6/12 pitch rises 6 inches for every 12 inches of horizontal run. That works out to 26.57° and a 50% grade. The second number is always 12 in this notation, so the pitch is described entirely by the first number.
What is the most common roof pitch?
Residential roofs most often fall between 4/12 and 9/12, with 6/12 among the most common. That range is steep enough to shed water and snow well, gentle enough to walk on, and compatible with standard asphalt shingles without extra underlayment.
How do I convert roof pitch to degrees?
Take the inverse tangent of the rise divided by 12: degrees = arctan(rise ÷ 12). A 4/12 pitch is arctan(4/12) = 18.43°, and a 12/12 pitch is exactly 45°. Doubling the pitch does not double the angle.
What is the minimum pitch for asphalt shingles?
Most manufacturers rate asphalt shingles down to 2/12, and between 2/12 and 4/12 they normally require a doubled underlayment. Below 2/12 shingles are generally not permitted at all and a membrane roofing system is used instead. Always follow the specific product instructions.
How do I work out rafter length from the pitch?
Multiply the horizontal run by √(1 + (rise ÷ 12)²). For a 12 ft run at 6/12, that is 12 × √(1 + 0.25) = 13.42 ft. This gives the sloped length from the wall to the ridge before any overhang, ridge-board deduction or plumb cut is allowed for.
What is the difference between pitch and slope on a roof?
In everyday use they are treated as the same thing, expressed as rise per 12 of run. Strictly, some references define pitch as rise over the full span rather than the run, which halves the number — so a 6/12 slope would be a 1/4 pitch. The rise-per-12 convention is what nearly everyone means today, and it is the one this roof pitch calculator uses throughout.