Roof Pitch Calculator
Convert roof pitch between ratio (X:12), degrees, and percent slope. Get the pitch multiplier, slope category, and a clear rise-over-run diagram.
Pick how you want to enter the pitch — the other two update automatically.
Vertical rise.
Horizontal run (usually 12).
Pitch conversions
- Pitch multiplier
- 1.1180
- Category
- Standard slope
- Asphalt shingles
- Suitable
Standard asphalt shingles are rated for this slope. Verify against current local codes.
How this calculator works
Roof pitch describes how steep a roof is, and it shows up in three different forms depending on who is talking: a contractor says “six twelve,” an architect's drawing lists degrees, and a grading or drainage spec uses percent slope. This calculator converts between all three instantly, and reports the two numbers that actually drive material orders: the pitch multiplier and the slope category.
Ratio, degrees, and percent
The ratio form is rise over run, normalized to a 12-inch run — a 6:12 roof climbs 6 inches for every 12 inches across. Degrees is the same slope expressed as the angle from horizontal, found with atan(rise / run). Percent slope is simply rise / run × 100, so a 6:12 roof is a 50% slope. Enter any one of the three and the other two update automatically, because they are all the same geometry described differently.
The pitch multiplier
A sloped roof has more surface than the floor beneath it. The pitch multiplier is the hypotenuse of the rise-over-run triangle, √(1 + (rise / run)²). Multiply a building's footprint by it to get the true roof area. A 6:12 roof has a 1.118 multiplier (about 12% more area than the footprint); a 12:12 roof has a 1.414 multiplier (about 41% more). Every material take-off — shingles, underlayment, ice-and-water shield — scales with this number.
Slope categories and shingle suitability
The calculator also labels the slope: below 2:12 is flat/low slope and requires membrane roofing, 2:12 to 4:12 is low slope (shingles allowed only with double underlayment), 4:12 to 9:12 is standard slope, 9:12 to 21:12 is steep, and anything above is very steep or mansard. These boundaries follow common roofing-trade practice and IRC R905.2.2 for asphalt shingle minimums. Always verify against current local codes before specifying materials.
Frequently asked questions
- What does "X:12" roof pitch mean?
- Roof pitch is written as rise over run, normalized to a 12-inch run. A "6:12" pitch rises 6 inches vertically for every 12 inches of horizontal distance. The run is almost always held at 12, so only the first number changes between roofs.
- What is the minimum roof pitch for asphalt shingles?
- Standard asphalt shingles are rated down to 4:12 with a single underlayment. Between 2:12 and 4:12 they are allowed only with a double layer of underlayment (IRC R905.2.2, ASTM D3462). Below 2:12, shingles are not permitted — use membrane roofing such as TPO, EPDM, or modified bitumen. Verify against current local codes.
- How do I measure roof pitch from the ground or attic?
- The easiest way is on a rafter in the attic: hold a level out horizontally, measure 12 inches along it, then measure straight down from the 12-inch mark to the rafter — that drop is your rise over a 12-inch run. From the ground, a digital level or a phone angle app sighted along the roof line gives a degree reading you can paste into the Degrees mode here.
- What is the most common residential roof pitch?
- Most homes fall between 4:12 and 9:12, which this calculator labels "Standard slope." It is walkable, sheds water and snow well, and works with virtually every shingle product. Steeper roofs (9:12 and up) are common in colder, higher-snow regions and on architectural styles like Tudor and Victorian.
- Why does pitch matter for roofing material costs?
- A steeper roof has more surface area than its footprint. The pitch multiplier captures this: a 6:12 roof has about 12% more area than the floor below it, and a 12:12 roof has about 41% more. More area means more shingles, underlayment, and labor — and steep roofs also require extra safety setup, which raises labor rates further.
- How does pitch affect snow load and drainage?
- Steeper roofs shed water and snow faster, reducing standing water, ice-dam risk, and the sustained snow load the structure carries. Low-slope roofs drain slowly and rely on the membrane and proper underlayment for water resistance, which is why shingles are not rated for them.