Roof pitch calculator
Roof pitch calculator for angle, multiplier, and rafter length.
Enter the rise and run, or an angle, to get the pitch as x/12, the angle in degrees, slope percent, and the pitch multiplier — plus common rafter length from the building width. A 6/12 roof is 26.57° with a 1.118 multiplier.
6 in rise over 12 in run
6/12 pitch
26.57° · 50% slope
Pitch multiplier
1.118x
sqrt(1 + (rise/12)²)
24 ft wide building
13 ft 5 in
common rafter, plate to ridge
Roof pitch chart
Pitch to degrees, slope, and multiplier
Every whole-number pitch from 1/12 to 12/12. Multiply a flat footprint area by the multiplier for roof area, or a rafter's horizontal run by it for rafter length.
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 |
| 2/12 | 9.46° | 16.7% | 1.014 |
| 3/12 | 14.04° | 25.0% | 1.031 |
| 4/12 | 18.43° | 33.3% | 1.054 |
| 5/12 | 22.62° | 41.7% | 1.083 |
| 6/12 | 26.57° | 50.0% | 1.118 |
| 7/12 | 30.26° | 58.3% | 1.158 |
| 8/12 | 33.69° | 66.7% | 1.202 |
| 9/12 | 36.87° | 75.0% | 1.250 |
| 10/12 | 39.81° | 83.3% | 1.302 |
| 11/12 | 42.51° | 91.7% | 1.357 |
| 12/12 | 45.00° | 100.0% | 1.414 |
Low slope changes the roofing
Under the International Residential Code, asphalt shingles are allowed only at 2/12 or steeper, and slopes from 2/12 up to 4/12 need double underlayment. Below 2/12, plan on a low-slope roofing system instead of shingles. Local code and the manufacturer's instructions govern.
Formula shown
How roof pitch, angle, and rafter length are calculated
1. Pitch from rise and run
pitch per 12 = rise / run x 12
2. Angle and slope
angle = atan(pitch / 12); slope % = pitch / 12 x 100
3. Pitch multiplier
multiplier = sqrt(1 + (pitch / 12)²)
4. Common rafter length
rafter = (span / 2 + overhang) x multiplier
Worked example: 24 ft wide gable at 6/12
Half the span is a 12 ft run. The ridge sits 12 x 6/12 = 6 ft 0 in above the wall plate. The rafter is 12 x 1.118 = 13 ft 5 in, and with a 12 in overhang it is 13 x 1.118 = 14 ft 6 3/8 in. Order the next stock length up and cut to fit.
What this does not include
Rafter size and spacing for snow and wind load, the ridge board deduction, bird's-mouth and tail cuts, and hip or valley rafters (which run at a different angle than common rafters). Have framing sized from span tables or by an engineer.
Next step
Use the pitch to estimate the roof
Pitch is the input that turns a flat footprint into real roof area. Carry it into the roofing calculator for squares and bundles, or the cost calculator for an installed range.
Sources
- International Residential Code, Chapter 9 Roof Assemblies — R905.2.2 minimum slope for asphalt shingles and low-slope underlayment
- NIST unit conversions — length units; pitch, angle, and multiplier are right-triangle geometry (Pythagorean theorem)
Sources checked
Checked against
Formulas and unit conversions checked against the sources listed on this page.
How we check our numbersLast updated: October 4, 2026
FAQ
Roof pitch calculator questions
Answers for calculating roof pitch, converting pitch to degrees, the pitch multiplier, rafter length, and minimum shingle slope.
How do you calculate roof pitch? + -
Roof pitch is the vertical rise for every 12 inches of horizontal run. Measure the rise over a known run, divide rise by run, and multiply by 12. A roof that rises 6 inches over 12 inches of run is a 6/12 pitch; one that rises 9 inches over 18 inches of run is also 6/12.
What angle is a 6/12 roof pitch? + -
A 6/12 pitch is 26.57 degrees from horizontal, a 50% slope, and has a pitch multiplier of 1.118. The angle is the arctangent of rise divided by run: atan(6 / 12).
What is the roof pitch multiplier? + -
The pitch multiplier (slope factor) is how much longer the sloped roof surface is than its flat footprint: sqrt(1 + (rise/12)^2). Multiply the flat footprint area by it to get roof area, or multiply a rafter's horizontal run by it to get the rafter length. A 4/12 pitch is 1.054, 6/12 is 1.118, 8/12 is 1.202, and 12/12 is 1.414.
How do I find rafter length from pitch? + -
Take half the building width as the rafter's horizontal run and multiply by the pitch multiplier. A 24 ft wide building at 6/12 has a 12 ft run, so the common rafter is about 13 ft 5 in from wall plate to ridge. Add the overhang run before multiplying, and deduct half the ridge board thickness when you cut.
What is the minimum roof pitch for asphalt shingles? + -
The International Residential Code allows asphalt shingles only on roof slopes of 2/12 or steeper, and slopes from 2/12 up to 4/12 require double underlayment. Check your local code and the shingle manufacturer's installation instructions before roofing a low-slope roof.
Is roof pitch the same as roof angle or slope? + -
They describe the same steepness in different units. Pitch is written as rise over 12 (6/12), angle is in degrees (26.57), and slope is a percentage (50%). This calculator converts between all three.