Roof Pitch Calculator
Calculate roof pitch ratio and slope angle from rise and run.
Calculate roof pitch ratio and slope angle from rise and run.
Roof pitch describes how steep a roof is, written as the inches of vertical rise for every 12 inches of horizontal run. A 6/12 roof climbs 6 inches over each foot of run, which works out to an angle of about 26.6 degrees. Roofers, framers, and inspectors use the X/12 format because it maps directly onto a framing square, while angle in degrees is handy for inclinometer apps, solar mounting, and some design software.
Pitch affects almost every part of a roofing project. It determines which materials are allowed, since standard asphalt shingles typically call for 4/12 or steeper while low-slope and flat roofs need membranes or specific metal systems. It changes how much material is needed, because a steeper roof covers more surface area over the same footprint. It affects safety and labor, as steeper roofs often need staging or roof brackets. People usually need the number when replacing a roof, ordering shingles, adding a dormer or porch roof that must match the existing slope, or planning skylights and solar panels.
To use this roof pitch calculator, enter the rise and the run in inches. A common method is to measure 12 inches level from a rafter or the roof surface and then measure straight up or down to find the rise, but any matching pair of measurements works because only the ratio matters. The tool divides rise by run, multiplies by 12 to express the result as X/12, and uses the arctangent of rise ÷ run to give the angle in degrees. For example, a rise of 9 inches over a run of 24 inches gives a 4.5/12 pitch at about 20.6 degrees.
The roof rises 6 inches for every 12 inches of horizontal run — about 26.6°.
Pitches up to 6/12 are generally walkable with proper footwear. Above 9/12 is steep and typically requires staging.
Results are estimates for planning purposes. Verify with product labels and local requirements before purchasing materials.
Roof pitch is the ratio of vertical rise to horizontal run, expressed as X/12. A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance toward the ridge.
The formula is: Pitch = (Rise ÷ Run) × 12
To convert pitch to degrees: Angle = arctan(Rise ÷ Run)
Enter your rise and run in the calculator above — any units work as long as they match, since the ratio is what matters.
| Pitch | Angle | Classification | Common application | Walkable? |
|---|---|---|---|---|
| 2/12 | 9.5° | Low slope | Flat-look modern, additions | With care |
| 3/12 | 14.0° | Low slope | Sheds, garage additions | With care |
| 4/12 | 18.4° | Moderate | Ranch homes, common residential | Yes |
| 5/12 | 22.6° | Moderate | Colonial, split-level homes | Yes |
| 6/12 | 26.6° | Standard | Most common US residential | Yes |
| 7/12 | 30.3° | Moderate steep | Farmhouse, craftsman styles | With caution |
| 8/12 | 33.7° | Steep | Cape Cod, colonial styles | Risky |
| 10/12 | 39.8° | Very steep | Victorians, chalet style | Staging needed |
| 12/12 | 45.0° | Very steep | Decorative gables, alpine | Staging needed |
| Material | Minimum pitch | Notes |
|---|---|---|
| Asphalt shingles | 4/12 standard (2/12 with special underlayment) | Most common material |
| Metal (standing seam) | 1/12 | Best choice for low slopes |
| Metal (exposed fastener) | 3/12 | More affordable metal option |
| Wood shakes | 4/12 | Require good ventilation |
| Slate | 4/12 | Heavy — needs structural assessment |
| Clay/concrete tile | 4/12 to 5/12 | Very heavy, needs engineer review |
| EPDM rubber (flat roof) | 0/12 to 1/12 | For very low or flat slopes only |
A steeper pitch means more roof surface area over the same building footprint. A 12/12 pitch has approximately 41% more surface area than a 4/12 pitch over the same base area.
Labor costs increase significantly above 8/12 because roofers require safety staging and work more slowly. Expect to pay 15–30% more in labor for pitches above 9/12 compared to standard 6/12 installations.
6/12 is the most common residential roof pitch in the US. It provides good water drainage, works with all standard roofing materials, and is walkable for most roofing work without staging.
Use a smartphone app with an inclinometer feature pointed at the roof slope to get the angle. Or, from inside the attic, hold a carpenter's level horizontally and measure up 12 inches on the level, then measure straight down to the rafter — that measurement is your rise.
Asphalt shingles require a minimum pitch of 4/12 for standard installation. Between 2/12 and 4/12, shingles can be used with special double-layer underlayment. Below 2/12 requires a flat roofing system.
Standing seam metal roofing can be installed on pitches as low as 1/12 with proper sealant. Exposed-fastener metal panels require a minimum 3/12 pitch. Metal roofing handles low slopes much better than asphalt shingles.
Steeper roofs require more material — a 12/12 pitch has significantly more surface area than a 4/12 pitch over the same building footprint. Installation labor costs also increase substantially above 8/12 due to safety requirements and staging.
A 4/12 roof pitch equals approximately 18.4 degrees. A 6/12 pitch is about 26.6 degrees. A 12/12 pitch is exactly 45 degrees.
Yes, a 6/12 pitch is generally walkable with proper rubber-soled footwear and caution. Anything above 8/12 typically requires roof brackets or staging for safe access. Never walk on a wet roof regardless of pitch.
The multiplier converts a flat footprint into actual sloped roof area and equals √(1 + (pitch ÷ 12)²): about 1.054 for 4/12, 1.118 for 6/12, and 1.414 for 12/12. A 1,500 sq ft footprint with a 6/12 roof has about 1,500 × 1.118 = 1,677 sq ft of roof surface before overhangs.