What is roof pitch?
Roof pitch is how steep a roof is, written as the number of inches it rises for every 12 inches of horizontal run. A 6/12 ("six-twelve") roof rises 6 inches for each foot you move inward. The same steepness can also be written as an angle in degrees or a percentage slope.
Angle = arctan(Rise ÷ Run)
Slope % = Rise ÷ Run × 100
Pitch multiplier = √(Rise² + Run²) ÷ Run
Example: you measure a rise of 8 inches over a 12-inch run.
- Pitch: 8/12
- Angle: arctan(8 ÷ 12) = 33.69°
- Slope: 8 ÷ 12 = 66.7%
- Multiplier: √(64 + 144) ÷ 12 = 1.202 — every square foot of floor plan needs 1.2 square feet of roofing.
Roof pitch chart
| Pitch | Angle | Slope | Multiplier | Typical use |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | Flat/low-slope membrane |
| 2/12 | 9.46° | 16.7% | 1.014 | Low slope: special underlayment |
| 3/12 | 14.04° | 25.0% | 1.031 | Low slope: metal, rolled roofing |
| 4/12 | 18.43° | 33.3% | 1.054 | Minimum for standard shingles |
| 5/12 | 22.62° | 41.7% | 1.083 | Common on ranch homes |
| 6/12 | 26.57° | 50.0% | 1.118 | Very common; walkable |
| 7/12 | 30.26° | 58.3% | 1.158 | Common residential |
| 8/12 | 33.69° | 66.7% | 1.202 | Steep; harness recommended |
| 9/12 | 36.87° | 75.0% | 1.250 | Steep |
| 10/12 | 39.81° | 83.3% | 1.302 | Steep |
| 12/12 | 45.00° | 100.0% | 1.414 | Steep (45°) |
| 16/12 | 53.13° | 133.3% | 1.667 | Very steep (A-frame, Victorian) |
How to measure roof pitch
From the attic (safest)
- Mark a point 12 inches along the bottom edge of a rafter using a level held horizontally.
- From that mark, measure straight up (vertically) to the underside of the rafter.
- That vertical measurement is the rise. If it's 7 inches, the roof is 7/12.
On the roof or at the gable end
Hold a 2-foot level horizontally with one end touching the roof surface, mark 12 inches along it, and measure vertically from the mark down to the roof. Only do this on low, walkable pitches and with proper fall protection.
From the ground
Measure the vertical height of the gable (from the top of the wall to the ridge) and half the building's width. Pitch = height ÷ half-width × 12. A gable 7.5 ft tall on a 30 ft wide house is 7.5 ÷ 15 × 12 = 6/12.
How to estimate roofing materials
Roofers measure in squares: one square covers 100 square feet of roof surface. Most architectural shingles come three bundles to a square.
Squares = Roof area ÷ 100 × (1 + Waste)
This works for both simple gable and hip roofs because every plane shares the same pitch. Add separately for dormers, porches or sections with a different pitch, and add roughly 10%–15% for waste, starter strips and ridge caps.
Why roof pitch matters
- Material choice: asphalt shingles need at least 2/12 (with double underlayment) and normally 4/12 or steeper. Below that, use membrane, rolled roofing or standing-seam metal.
- Cost: steep roofs (above about 8/12) cost more to install because crews need extra safety equipment and work more slowly.
- Drainage and snow: steeper roofs shed water and snow faster; low-slope roofs need careful detailing to avoid leaks.
- Attic space and solar: steeper pitches create usable attic room. Solar panels generally perform well on most pitches from about 4/12 to 9/12.
Frequently asked questions
What angle is a 6/12 roof pitch?
26.57 degrees (arctan of 6 ÷ 12). Its slope is 50%.
What is the most common roof pitch?
Most US homes have pitches between 4/12 and 9/12, with 6/12 being one of the most common because it balances cost, drainage and walkability.
How do I convert roof pitch to degrees?
Divide the rise by 12 and take the inverse tangent (arctan). For 4/12: arctan(0.333) = 18.43°.
What is the minimum pitch for shingles?
Asphalt shingles can be installed down to 2/12 with a double layer of underlayment, but most manufacturers recommend 4/12 or steeper for standard installation.
How many squares is my roof?
Multiply the building footprint (including overhangs) by the pitch multiplier and divide by 100. A 42 × 32 ft footprint at 6/12 (multiplier 1.118) is about 1,503 sq ft, or 15 squares before waste.