Roof pitch calculator
Roof pitch, angle, slope and rafter length from a measurement, an angle or the roof's height.
Roof pitch
6/12 rise per 12 of run
- Angle
- 26.6°
- Slope
- 50.0%
- Pitch multiplier
- 1.118
- Rafter length
- 14 ft 6 3/8 in
- Roof rise (plate to peak)
- 6 ft 0 in
Rafter length is the line length to the end of the overhang (14.53 ft), before subtracting half the ridge board and adding plumb cuts.
How to calculate roof pitch
Roof pitch is how many inches the roof rises for every 12 inches it runs horizontally, written like 6/12. The angle, slope and rafter length all follow from it.
- Pitch = rise ÷ run × 12 (or roof height ÷ half the building width × 12 for a gable)
- Angle = arctangent(pitch ÷ 12)
- Slope = pitch ÷ 12 × 100%
- Multiplier = √(1 + (pitch ÷ 12)²)
- Rafter length = (half the width for a gable, the full width for a shed, plus overhang) × multiplier
Worked example
A roof that rises 6 inches over 12 inches is 6/12. The angle is arctan(6 ÷ 12) = 26.6° and the multiplier is 1.118. On a 24 ft gable with a 12 inch overhang, each rafter runs 12 + 1 = 13 ft, so the rafter is 13 × 1.118 = 14.53 ft (14 ft 6 3/8 in).
Roof pitch chart
Common pitches with their angle, slope and multiplier. Multiply a roof's flat (plan) area by the multiplier to get its sloped area.
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 |
| 2/12 | 9.46° | 16.7% | 1.014 |
| 3/12 | 14.04° | 25.0% | 1.031 |
| 4/12 | 18.43° | 33.3% | 1.054 |
| 5/12 | 22.62° | 41.7% | 1.083 |
| 6/12 | 26.57° | 50.0% | 1.118 |
| 7/12 | 30.26° | 58.3% | 1.158 |
| 8/12 | 33.69° | 66.7% | 1.202 |
| 9/12 | 36.87° | 75.0% | 1.250 |
| 10/12 | 39.81° | 83.3% | 1.302 |
| 11/12 | 42.51° | 91.7% | 1.357 |
| 12/12 | 45.00° | 100.0% | 1.414 |
| 14/12 | 49.40° | 116.7% | 1.537 |
| 16/12 | 53.13° | 133.3% | 1.667 |
| 18/12 | 56.31° | 150.0% | 1.803 |
| 24/12 | 63.43° | 200.0% | 2.236 |
Minimum roof pitch by material
From the International Residential Code (IRC) R905.2.2 and R905.10.2. Local codes and the manufacturer's instructions can require more, so check with your building department.
| Roofing | Minimum pitch | Notes |
|---|---|---|
| Asphalt shingles | 2/12 | Double underlayment from 2:12 up to 4:12. IRC R905.2.2 |
| Metal panels, lapped seams without sealant | 3/12 | IRC R905.10.2 |
| Metal panels, lapped seams with applied lap sealant | 0.5/12 | Sealant per the manufacturer's instructions. IRC R905.10.2 |
| Metal panels, standing seam | 0.25/12 | IRC R905.10.2 |
Roof pitch questions
What does a roof pitch like 6/12 mean?
The roof rises 6 inches for every 12 inches it runs horizontally. The first number is the rise; the 12 is always the run, so a bigger first number means a steeper roof.
How do I measure roof pitch?
From the attic or at a gable end, hold a level against the underside of a rafter, mark 12 inches along the level, and measure straight up (or down) from that mark to the rafter: that's the rise. Choose "Rise and run" above and enter it. You can also measure the roof's height and the building's width and choose "Roof height". Stay off steep or wet roofs.
What is a 6/12 roof pitch in degrees?
26.57°. A 4/12 roof is 18.43°, an 8/12 roof is 33.69°, and a 12/12 roof is 45°. The chart above lists every common pitch.
What is the roof pitch multiplier?
The length along the slope for each foot of horizontal run: √(1 + (pitch ÷ 12)²). For a 6/12 roof it's 1.118, so a rafter that runs 10 feet horizontally is 11.18 feet long, and a roof covering 1,000 square feet of floor plan has about 1,118 square feet of roof surface before overhangs.
What is the minimum pitch for a metal or shingle roof?
Under the IRC, asphalt shingles need at least 2/12, with double underlayment below 4/12. Metal panels range from 0.25/12 for standing seam to 3/12 for lapped seams without sealant. See the table above, and check your local code and the product's instructions.
How do I calculate a shed roof pitch?
A shed roof has one slope across the full width, so the rafter runs the whole width instead of half. Choose "Shed" as the roof type; with "Roof height", enter how much higher the tall wall is than the short one.