How to measure your roof pitch safely
You do not need to climb onto the roof. Pick whichever of these methods is easiest for your house.
From the attic
- Take a level that is at least 12 inches long and a tape measure into the attic.
- Hold one end of the level against the underside of a rafter and make it level.
- Mark the level at 12 inches from the rafter.
- Measure straight up from that mark to the underside of the rafter. That number is your rise. If it is 6 inches, the pitch is 6/12.
From a gable end or ladder
- From a ladder at the gable end, place a level against the edge of the roof (the rake board) so it sticks out level.
- At 12 inches along the level, measure up to the roof edge. That is the rise per 12.
From the overall shape
If you know the total height from the top of the wall to the ridge, and half the width of the building, enter those as rise and run. For example, a ridge 5 ft above a wall on a building 30 ft wide has a rise of 5 ft over a run of 15 ft, which is a 4/12 pitch.
How pitch, angle and slope are related
Pitch = rise ÷ run × 12 (written as x/12)
Angle = arctan(rise ÷ run)
Slope percent = rise ÷ run × 100
Pitch factor = √(1 + (rise ÷ run)²)
All four describe the same thing. Pitch is how roofers talk, angle is how a speed square or phone app reads it, slope percent is common on plans, and the pitch factor is what you multiply a footprint by to get the real roof area.
Worked examples
Rise 6 in over a run of 12 in
Pitch 6/12. Angle = arctan(0.5) = 26.6°. Slope = 50%. Pitch factor = √(1 + 0.25) = 1.118.
Rise 5 ft over a run of 15 ft
Rise ÷ run = 0.333, so the pitch is 0.333 × 12 = 4/12. Angle = arctan(0.333) = 18.4°. Pitch factor 1.054.
Roof pitch chart
| Pitch | Angle | Slope | Pitch factor | What it means |
|---|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 | Low slope; membrane roofing |
| 2/12 | 9.5° | 16.7% | 1.014 | Lowest for shingles, with extra underlayment |
| 3/12 | 14.0° | 25.0% | 1.031 | Low slope |
| 4/12 | 18.4° | 33.3% | 1.054 | Common on ranch houses |
| 5/12 | 22.6° | 41.7% | 1.083 | Conventional |
| 6/12 | 26.6° | 50.0% | 1.118 | Very common; walkable |
| 7/12 | 30.3° | 58.3% | 1.158 | Conventional |
| 8/12 | 33.7° | 66.7% | 1.202 | Walk with care |
| 9/12 | 36.9° | 75.0% | 1.250 | Starting to get steep |
| 10/12 | 39.8° | 83.3% | 1.302 | Steep; roof jacks needed |
| 12/12 | 45.0° | 100% | 1.414 | Steep |
| 18/12 | 56.3° | 150% | 1.803 | Very steep; specialist work |
Why roof pitch matters
- Material choice. Shingles need a minimum slope to shed water. Very low roofs need membranes; very steep roofs may need extra nails per shingle.
- How much material. The steeper the roof, the more surface there is to cover. A 12/12 roof needs about 41% more shingles than its footprint suggests.
- Price. Roofers usually charge more for steep roofs because the work is slower and needs safety equipment.
- Safety. Pitch decides whether a roof can be walked on at all.
Common mistakes to avoid
- Measuring the run along the slope. The run is level distance. Measure along a level, not along the rafter.
- Using the whole building width as the run. On a simple gable roof, the run for each side is half the width.
- Mixing units. Rise in feet and run in inches gives a wildly wrong pitch. Use the unit menus so both match what you measured.
- Trusting a phone app on a curved board. Rafter edges and fascia boards are not always straight. Check the reading in two or three places.
Frequently asked questions
What does a 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches it runs horizontally. That is an angle of about 26.6 degrees and a 50% slope. It is one of the most common pitches on US houses.
How do I convert roof pitch to degrees?
Divide the rise by 12 and take the arctangent. For a 6/12 pitch, arctan(6 ÷ 12) = 26.6°. A 4/12 pitch is 18.4°, 8/12 is 33.7° and 12/12 is exactly 45°.
What is the minimum pitch for asphalt shingles?
Asphalt shingle makers generally allow shingles down to 2/12, but between 2/12 and 4/12 they require extra underlayment protection. Below 2/12 you need a low-slope roofing system. Always follow the instructions on the shingle wrapper.
What is a pitch factor?
The number you multiply a flat roof footprint by to get the real, sloped roof area. It is √(1 + (rise ÷ 12)²). A 6/12 roof has a pitch factor of 1.118, so it is 11.8% bigger than its footprint.
Is roof pitch the same as roof slope?
People use both words for the same thing. Strictly, pitch is usually given as rise per 12 (6/12) and slope as a percent or ratio (50%, or 1:2). This calculator shows all of them.
What is a walkable roof pitch?
Roofers generally consider up to about 6/12 comfortable to walk and up to about 8/12 or 9/12 walkable with care. Steeper roofs need roof jacks or a harness. If you are unsure, stay off the roof and measure from the attic or a gable end.