Roof Pitch Calculator
Convert rise and run into roof pitch, slope angle, area multiplier, and hip/valley rafter factor.
Vertical rise measured over the run below.
Horizontal run. Use 12 to read pitch directly, or enter the real run in inches to also get rafter length.
Optional - enter the flat (footprint) area to get true sloped roof area.
Your Roof Pitch
- Measure the rise - hold a level out horizontally and measure down to the roof at the 12-inch mark, or use any rise over a known run.
- Keep run at 12 - leaving run at 12 reads the pitch directly - e.g. 6 rise / 12 run = a 6/12 roof.
- Read the multiplier - the area multiplier converts a flat footprint into true sloped surface area.
- Add area for sloped surface - open Advanced and enter your flat footprint to get the sloped area directly.
- Use the hip/valley factor - multiply the horizontal run of a hip or valley by this factor to get its rafter length.
A 6/12 roof - 6 inches of rise for every 12 inches of run - sits at 26.57 degrees, a 50 percent grade, and an area multiplier of 1.118. That multiplier is the number that matters: a 1,500 sq ft footprint under a 6/12 roof is about 1,677 sq ft of actual roof surface, so you order shingles for the 1,677, never the 1,500. Enter your rise and run above to get pitch, angle, grade, and both the common-rafter and hip/valley multipliers.
Reading a Roof Pitch
Understanding Roof Pitch
Roof pitch is the rise in inches for every 12 inches of horizontal run. A 6/12 roof rises 6 inches per foot of run, which works out to a 26.6° angle. Pitch determines what roofing products you can use, how much surface area (and therefore material) a roof actually has, and how safe it is to walk.
The slope multiplier is the practical payoff: it converts the flat footprint area into the real sloped area. A 12/12 roof has about 41% more surface than its footprint, so the same house plan needs far more shingles under a steep roof than a shallow one. For hips and valleys, the hip/valley multiplier does the same job for the diagonal rafters that run up the corners.
Roof Pitch Reference Table
Pitch, angle, and multipliers from 1/12 to 12/12:
| Pitch | Angle | Area Multiplier | Hip/Valley Factor |
|---|---|---|---|
| 1/12 | 4.8° | 1.003 | 1.417 |
| 2/12 | 9.5° | 1.014 | 1.424 |
| 3/12 | 14.0° | 1.031 | 1.436 |
| 4/12 | 18.4° | 1.054 | 1.453 |
| 5/12 | 22.6° | 1.083 | 1.474 |
| 6/12 | 26.6° | 1.118 | 1.500 |
| 7/12 | 30.3° | 1.158 | 1.530 |
| 8/12 | 33.7° | 1.202 | 1.564 |
| 9/12 | 36.9° | 1.250 | 1.601 |
| 10/12 | 39.8° | 1.302 | 1.642 |
| 11/12 | 42.5° | 1.357 | 1.685 |
| 12/12 | 45.0° | 1.414 | 1.732 |
Multiply a flat footprint by the area multiplier to get sloped roof area. Multiply a hip or valley's horizontal run by the hip/valley factor to get its rafter length.
Roof Pitch Formulas
How each value is derived:
Slope angle = arctangent(Rise ÷ Run)
Area multiplier = √(Rise² + Run²) ÷ Run
Hip/valley factor = √((Rise ÷ Run)² + 2)
Sloped area = Flat footprint area × Area multiplier
The area multiplier is also the common-rafter length factor: multiply the horizontal run of a common rafter by it to get the rafter length.
How to Measure Roof Pitch
You do not need to climb onto the roof to measure pitch. The most accurate way is from inside the attic: hold a level out horizontally against the underside of a rafter, mark 12 inches along the level, then measure straight down from that mark to the rafter. That vertical distance in inches is your rise over a 12 inch run - enter it above with run set to 12.
From the eave you can read pitch with a speed square: rest it against a rafter tail with the pivot on the edge, let it swing until the level bubble centers, and read the pitch scale where it crosses the board. A phone inclinometer app works in a pinch, but treat it as an estimate - most are only good to about a degree, which is fine for picking materials but not for cutting rafters.
Minimum Pitch by Roofing Material
Every roof covering has a lowest slope it can shed water on. Go below it and water works back up under the material. These are the common IRC minimums (rise in 12 inches of run):
| Material | Minimum Pitch | Notes |
|---|---|---|
| Asphalt shingles | 2 / 12 | From 2/12 up to 4/12 needs a doubled or self-adhering underlayment; 4/12 and up is standard single-underlayment (R905.2.2). |
| Clay / concrete tile | 2.5 / 12 | Heavy material, so the framing must be sized for the load as a separate check (R905.3). |
| Metal shingles | 3 / 12 | Lapped exposed-fastener panels also start around 3/12 (R905.4). |
| Standing-seam metal | 1/4 / 12 | Sealed seams shed water on near-flat roofs; confirm the exact panel profile (R905.10). |
| Wood shingles / shakes | 3 / 12 | Cedar needs slope to drain and to dry between courses (R905.7, R905.8). |
| Slate | 4 / 12 | Very heavy; framing capacity is a separate structural check (R905.6). |
| Mineral roll roofing | 1 / 12 | Utility and low-slope sheds; not a finished-home look (R905.5). |
| Built-up / membrane (TPO, EPDM) | 1/4 / 12 | Low-slope and near-flat roofs; this is membrane territory, not shingles (R905.9). |
When a roof lands between 2/12 and 4/12, asphalt shingles are still allowed but the code requires a doubled underlayment or a self-adhering membrane underneath. Below 2/12, switch to a membrane roof entirely.
Code Notes
- Asphalt shingles are permitted only on roof slopes of 2 in 12 or steeper. Below 2/12 the roof sheds water too slowly and it backs up under the shingle tabs, so low-slope roofs need a membrane system instead.IRC 2021 Section R905.2.2 - Asphalt Shingle Slope
- On slopes from 2/12 up to 4/12 the same section requires a doubled underlayment or a self-adhering membrane under the shingles. At 4/12 and above a single underlayment layer is allowed, one practical reason steeper roofs are simpler to detail and slightly cheaper to underlay.IRC 2021 Section R905.2.2 - Low-Slope Underlayment
Next Steps
Pitch is the first input for every other roofing number. Once you have it:
Related Calculators
Pitch is the first number in any roofing estimate - once you have it, size your materials in the construction calculator collection.
Frequently Asked Questions
What is the most common residential roof pitch?
Most homes fall between 4/12 and 9/12. A 4/12 roof (18.4°) is a common builder-grade minimum for shingles, while 6/12 to 8/12 is typical for steeper traditional designs. Anything below 2/12 is considered low-slope and usually needs membrane roofing instead of shingles.
How do I measure roof pitch without climbing on the roof?
From inside the attic, hold a level horizontally against a rafter, measure 12 inches along it, then measure straight down from the level to the rafter at that point. That vertical measurement is your rise over a 12-inch run - enter it as the rise with run set to 12.
What does the area multiplier do?
It converts a flat (footprint) area into the actual sloped roof area. A 1,500 ft² footprint under a 6/12 roof (multiplier 1.118) has about 1,677 ft² of roof surface. Use the sloped area, never the footprint, when ordering shingles.
What is the hip and valley multiplier for?
Hip and valley rafters run diagonally up the corners of a roof, so they are longer than common rafters. Multiply the horizontal run of the hip or valley by this factor to get its length. For a 6/12 roof the factor is 1.500.
Can you walk on a 12/12 roof?
A 12/12 roof is a 45° slope - too steep to walk safely without roof jacks, staging, or a harness. Pitches up to about 7/12 are generally walkable for experienced roofers; above that, fall protection and staging become necessary.
What is a 6/12 roof pitch in degrees?
A 6/12 pitch works out to 26.57 degrees, which is why tables round it to 26.6. The angle is the arctangent of rise over run: arctan(6 divided by 12) = 26.57 degrees. The same roof is a 50 percent grade, because the rise is half the run.
What roof pitch do I need for asphalt shingles?
The IRC allows asphalt shingles on any slope of 2/12 or steeper. From 2/12 up to 4/12 the code requires a doubled underlayment or a self-adhering membrane; at 4/12 and above a single underlayment layer is fine. Below 2/12 you are in low-slope territory and need a membrane roof such as TPO or EPDM instead of shingles.