Roof Pitch Calculator
Convert rise over run into degrees and percent grade, and get rafter length, hip rafter, cut angles, roof area and shingle bundles in one go.
Measurements
Results
- Pitch
- 6.00/12
- Angle
- 26.57°
- Grade
- 50.0%
- Rafter length
- 18.45 ft
- Roof area (both slopes)
- 1,476 sq ft
Rafter in feet & inches: 18 ft 5 6/16 in
Steep-ish — use roof jacks and soft-soled boots
Everything else this roof gives you
- Rise at ridge
- 7.50 ft
- Run (half span)
- 15.00 ft
- Run + overhang
- 16.50 ft
- Rafter multiplier
- 1.1180
- Hip / valley rafter
- 22.500 ft
- Plumb cut
- 63.43°
- Seat (birdsmouth) cut
- 26.57°
- Roof area
- 1,476 sq ft
- Squares (100 sq ft)
- 14.8
- Shingle bundles (3/sq)
- 45
Squares and bundles assume US shingle sizing, so they are quoted in square feet even when you work in metres.
Quick answer
Roof pitch is the rise in inches for every 12 inches of horizontal run. A 6/12 pitch equals 26.57° and a 50% grade, and its rafter multiplier of 1.1180 means the roof surface is about 12% larger than the flat footprint underneath it.
pitch = rise / 12 · angle = arctan(rise ÷ run) · rafter = √(rise² + run²)
How to use the roof pitch calculator
- 1Pick how you know the slope — rise per 12 inches, degrees, or percent grade — then type that value.
- 2Enter the building span wall to wall; the calculator halves it to get the run automatically.
- 3Add the eave overhang so the rafter length includes the tail that projects past the wall.
- 4Enter the ridge length to get the true roof area, squares and shingle bundle count.
- 5Read the pitch, angle, grade, rafter length and cut angles, then copy the results for your order or quote.
Roof pitch to angle chart
Every common pitch with its angle in degrees, percent grade and the rafter multiplier that converts flat area into true roof area.
| Pitch | Angle | Grade | Rafter multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.0035 |
| 2/12 | 9.46° | 16.7% | 1.0138 |
| 3/12 | 14.04° | 25.0% | 1.0308 |
| 4/12 | 18.43° | 33.3% | 1.0541 |
| 5/12 | 22.62° | 41.7% | 1.0833 |
| 6/12 | 26.57° | 50.0% | 1.1180 |
| 7/12 | 30.26° | 58.3% | 1.1577 |
| 8/12 | 33.69° | 66.7% | 1.2019 |
| 9/12 | 36.87° | 75.0% | 1.2500 |
| 10/12 | 39.81° | 83.3% | 1.3017 |
| 11/12 | 42.51° | 91.7% | 1.3566 |
| 12/12 | 45.00° | 100.0% | 1.4142 |
| 14/12 | 49.40° | 116.7% | 1.5366 |
| 16/12 | 53.13° | 133.3% | 1.6667 |
| 18/12 | 56.31° | 150.0% | 1.8028 |
Choosing a pitch: what roofers watch for
- Under 3/12 (low slope): water drains slowly — use membrane, standing seam, or shingles rated for low slope with a doubled underlayment.
- 4/12 to 6/12: the sweet spot — cheap to frame, safe to walk, compatible with almost every roof covering.
- 7/12 to 9/12: sheds snow well and gives usable attic headroom, but material and labour costs climb with the multiplier.
- 10/12 and steeper: dramatic and self-clearing in snow country; expect staging, harness work and 30–50% more surface area than the footprint.
Worked example
A 30 ft span gable with a 6/12 pitch, 1.5 ft overhang and a 40 ft ridge: the run is 15 ft, so the rise is 7.5 ft and the rafter to the wall plate is √(15² + 7.5²) = 16.77 ft. Adding the overhang gives a 16.5 ft run and an 18.45 ft rafter. Two 40 ft slopes make about 1,476 sq ft of roof — 14.8 squares, or 45 bundles of three-bundle shingles.
Frequently asked questions
What is roof pitch?
Roof pitch is the vertical rise of a roof for every 12 inches of horizontal run, written as a fraction like 6/12. A 6/12 roof climbs 6 inches for each foot it travels inward, which equals 26.57 degrees or a 50% grade.
How do I calculate roof pitch in degrees?
Divide the rise by the run and take the arctangent: angle = arctan(rise ÷ run). For a 6/12 roof that is arctan(6 ÷ 12) = 26.57°. This calculator converts both ways, so you can also enter degrees and read the pitch back as x/12.
How do I measure the pitch of an existing roof?
Hold a level horizontally against a rafter, mark 12 inches along the level, then measure straight up from that mark to the roof. That vertical measurement is the rise per 12. A smartphone inclinometer held on a rafter works too — enter the reading in degrees mode.
What is the most common roof pitch?
Most US homes fall between 4/12 and 9/12, with 6/12 the usual compromise between shedding water and staying walkable. Anything under 3/12 counts as low slope and needs a membrane or shingles specifically rated for it.
What is the minimum roof pitch for shingles?
Asphalt shingles are normally rated down to 2/12 with a doubled underlayment, and 4/12 or steeper for standard single-layer application. Confirm against the manufacturer's instructions and local code, because warranty cover depends on it.
What roof pitch is walkable?
Up to about 6/12 (26.57°) most roofers walk the surface in soft-soled boots. From 7/12 to 9/12 roof jacks help, and 10/12 or steeper normally needs a harness or scaffold. The calculator flags which band your slope falls into.
How does pitch change the amount of roofing material I need?
Multiply the flat footprint area by the rafter multiplier for your pitch. A 6/12 roof has a multiplier of 1.1180, so a 2,000 sq ft footprint carries about 2,236 sq ft of roof surface — roughly 22.4 squares of shingles.
Is roof pitch the same as roof slope?
In everyday use they are interchangeable. Strictly, pitch is rise over the total span while slope is rise over run per 12 inches. Suppliers and framers all quote the x/12 rise-over-run figure, which is what this tool uses.