How to calculate roof pitch
Roof pitch is how many inches the roof rises for every 12 inches it runs horizontally. Divide the rise by the run and multiply by 12:
Pitch = rise ÷ run × 12 · Angle = arctan(rise ÷ run) · Slope % = rise ÷ run × 100
Example. A roof rises 4 ft over a horizontal run of 8 ft. 4 ÷ 8 × 12 = 6, so it is a 6/12 pitch (said "6 in 12"). The angle is arctan(0.5) = 26.57° and the slope is 50%.
Rise and run can be in any unit as long as both are the same. In metric, 250 mm of rise per 1,000 mm of run is a 3/12 pitch, or 14.04°. Outside the US and Canada pitch is usually given in degrees, which is why the calculator shows both.
Roof pitch chart
Common pitches with their angle, slope, the multiplier that turns a flat footprint into roof area, and the rafter length for each foot of horizontal run.
| Pitch | Degrees | Slope | Multiplier | Rafter per ft of run |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 12.04 in |
| 2/12 | 9.46° | 16.7% | 1.014 | 12.17 in |
| 3/12 | 14.04° | 25.0% | 1.031 | 12.37 in |
| 4/12 | 18.43° | 33.3% | 1.054 | 12.65 in |
| 5/12 | 22.62° | 41.7% | 1.083 | 13.00 in |
| 6/12 | 26.57° | 50.0% | 1.118 | 13.42 in |
| 7/12 | 30.26° | 58.3% | 1.158 | 13.89 in |
| 8/12 | 33.69° | 66.7% | 1.202 | 14.42 in |
| 9/12 | 36.87° | 75.0% | 1.250 | 15.00 in |
| 10/12 | 39.81° | 83.3% | 1.302 | 15.62 in |
| 11/12 | 42.51° | 91.7% | 1.357 | 16.28 in |
| 12/12 | 45.00° | 100.0% | 1.414 | 16.97 in |
| 14/12 | 49.40° | 116.7% | 1.537 | 18.44 in |
| 16/12 | 53.13° | 133.3% | 1.667 | 20.00 in |
| 18/12 | 56.31° | 150.0% | 1.803 | 21.63 in |
| 24/12 | 63.43° | 200.0% | 2.236 | 26.83 in |
Degrees to roof pitch
To go from an angle to pitch, take the tangent of the angle and multiply by 12. A 30° roof is 12 × tan 30° = 6.93, so about a 7/12 pitch.
| Angle | Pitch | Nearest | Slope |
|---|---|---|---|
| 5° | 1.05/12 | 1/12 | 8.7% |
| 10° | 2.12/12 | 2/12 | 17.6% |
| 12° | 2.55/12 | 2½/12 | 21.3% |
| 15° | 3.22/12 | 3¼/12 | 26.8% |
| 18° | 3.90/12 | 4/12 | 32.5% |
| 20° | 4.37/12 | 4¼/12 | 36.4% |
| 22.5° | 4.97/12 | 5/12 | 41.4% |
| 25° | 5.60/12 | 5½/12 | 46.6% |
| 30° | 6.93/12 | 7/12 | 57.7% |
| 35° | 8.40/12 | 8½/12 | 70.0% |
| 40° | 10.07/12 | 10/12 | 83.9% |
| 45° | 12.00/12 | 12/12 | 100.0% |
| 50° | 14.30/12 | 14¼/12 | 119.2% |
| 60° | 20.78/12 | 20¾/12 | 173.2% |
How to measure your roof pitch
- On the roof. Hold a 2 ft level flat on the shingles with one end touching. Mark 12 inches from that end, then measure straight down from the mark to the roof. That number is the rise per 12.
- In the attic. Hold the level against the bottom edge of a rafter, mark 12 inches, and measure from the mark up to the rafter. Attic rafters give the same pitch as the roof surface without climbing.
- From the gable end. Measure the height from the top of the wall to the peak and half the building width. Enter them as rise and run.
- With a phone. Lay the phone on a rafter or the roof and read the angle in a level app, then choose Angle above.
- With a speed square. Set the pivot on the roof edge and read the pitch scale where the square meets the plumb line.
Roof height and rafter length from pitch
Once you know the pitch and the building width, the height of the roof and the length of the rafters follow from the same triangle. On a gable roof the run is half the width. On a lean-to or shed roof the run is the full width.
Roof height = run × pitch ÷ 12 · Rafter length = run × multiplier
Example. A 24 ft wide house with a 6/12 gable roof has a 12 ft run. The ridge sits 6 ft above the top of the wall, and each rafter is 13 ft 5 in from wall to ridge, or 14 ft 6⅜ in with a 12 inch horizontal overhang. Framers subtract half the thickness of the ridge board from the run before cutting. Choose Span & pitch above for your building.
Minimum roof pitch by material
Every roofing material has a lowest pitch it can shed water at. These are the minimums in the International Residential Code (IRC), which most US jurisdictions adopt. Manufacturer instructions and local codes can be stricter, and below about 2/12 a roof is treated as low slope and needs a membrane.
| Material | Minimum pitch | Note |
|---|---|---|
| Asphalt shingles | 2/12 (9.5°) | Double underlayment below 4/12 |
| Metal shingles | 3/12 (14.0°) | |
| Wood shingles and shakes | 3/12 (14.0°) | |
| Clay or concrete tile | 2½/12 (11.8°) | Double underlayment below 4/12 |
| Slate | 4/12 (18.4°) | |
| Standing seam metal | ¼/12 (1.2°) | |
| Lapped metal panels | 3/12 (14.0°) | 1/2:12 allowed with lap sealant |
| Built-up, TPO, EPDM | ¼/12 (1.2°) |
Shingles on a 2/12 to 4/12 pitch are allowed with two layers of underlayment, but many roofers prefer metal or a membrane on porches and lean-tos that shallow.
Common roof pitches
- Low slope, 2/12 to 4/12. Porches, sheds, additions, carports, ranch homes and many manufactured homes.
- Conventional, 4/12 to 9/12. Most US houses. 6/12 is a very common choice for new homes because it is walkable and sheds water well.
- Steep, above 9/12. Two-story colonials, Tudors, A-frames and snowy regions. A 12/12 pitch is 45°.
Roofers generally consider pitches up to about 6/12 walkable. From 7/12 or 8/12 upward they need roof jacks or harnesses and usually charge more, and the roof area itself grows with the multiplier, which the roofing calculator uses to estimate squares, shingle bundles and replacement cost.
Pitch for snow, metal roofs and solar panels
Steeper roofs shed snow and water faster, which is why heavy-snow regions favor 8/12 and above. Metal roofs shed snow at lower pitches than shingles. Standing seam metal can go as low as 1/4:12, while exposed-fastener panels need 3/12 unless the laps are sealed. For solar panels mounted flush to the roof, most pitches between 4/12 and 9/12 (18° to 37°) work well; the ideal fixed tilt is close to your latitude.