Roof pitch describes how steep a roof is. In North America it is usually expressed as the amount of vertical rise in inches for every 12 inches of horizontal run, for example 6:12. It can also be expressed as an angle in degrees or as a percent slope.

How do I convert roof pitch to degrees?

To convert roof pitch to degrees, first express the pitch as rise over run (for example 6:12 becomes 6/12 = 0.5). Then use the formula angle = arctan(rise/run). For a 6:12 roof, angle = arctan(0.5) ≈ 26.57°.

How do I calculate rafter length from roof pitch?

If you know the rise and run, rafter length is the hypotenuse of the right triangle: rafter length = √(rise² + run²). If you know the building span and pitch, the run is half the span and the rise is run × pitch ratio.

What roof pitch is considered walkable?

Many contractors consider roofs up to about 6:12 pitch to be walkable with care and proper footwear. Steeper roofs often require roof jacks, harnesses, or scaffolding. Always follow local safety regulations and manufacturer recommendations.

What is a good roof pitch for snow or heavy rain?

In snowy climates, steeper pitches such as 8:12 or higher help shed snow. In areas with heavy rain but little snow, moderate pitches like 4:12 to 6:12 are common. The ideal pitch also depends on roofing material and local building codes.

Roof Pitch Calculator – Slope, Angle, Rise, Run & Rafter Length

What is roof pitch?

Roof pitch describes how steep a roof is. In North America it is usually written as rise in inches per 12 inches of run, for example 6:12. The higher the first number, the steeper the roof.

Roof pitch can be expressed in several equivalent ways:

Pitch (x:12) – e.g. 4:12, 6:12, 12:12
Angle in degrees – angle between roof surface and horizontal
Percent slope – rise ÷ run × 100
Rise / run ratio – e.g. 1:3, 0.5:1

Roof pitch formulas

From rise and run

Let \(r\) be rise and \(h\) be run (horizontal):

Pitch (x:12): \( \text{pitch} = \dfrac{r}{h} \times 12 \)
Angle (degrees): \( \theta = \arctan\!\left(\dfrac{r}{h}\right) \times \dfrac{180}{\pi} \)
Percent slope: \( \%\text{slope} = \dfrac{r}{h} \times 100 \)
Rafter length: \( L = \sqrt{r^2 + h^2} \)

From pitch (x:12)

If pitch is \(p\) (e.g. 6 for 6:12):

Rise / run ratio: \( \dfrac{r}{h} = \dfrac{p}{12} \)
Angle: \( \theta = \arctan\!\left(\dfrac{p}{12}\right) \times \dfrac{180}{\pi} \)
Percent slope: \( \%\text{slope} = \dfrac{p}{12} \times 100 \)

From angle

Rise / run ratio: \( \dfrac{r}{h} = \tan(\theta) \)
Pitch (x:12): \( p = 12 \times \tan(\theta) \)
Percent slope: \( \%\text{slope} = 100 \times \tan(\theta) \)

Typical roof pitches

Common roof pitch ranges (exact values depend on climate, material, and local codes):

Pitch (x:12)	Angle (°)	Percent slope	Typical use
1:12 – 3:12	4.8° – 14°	8% – 25%	Low-slope roofs, some metal or membrane systems
4:12 – 6:12	18° – 27°	33% – 50%	Common residential asphalt shingle roofs
7:12 – 9:12	30° – 37°	58% – 75%	Steeper roofs, better snow shedding
10:12 – 12:12	40° – 45°	83% – 100%	Very steep roofs, strong visual impact

How to measure roof pitch in the field

From the roof surface (using a level)
- Place a 12" (or 30 cm) level horizontally on the roof.
- Hold it level, then measure vertically from the roof surface up to the underside of the level at the outer end.
- The vertical measurement in inches is the pitch (x:12). For example, 6" rise over 12" run is 6:12.
From inside the attic
- Measure the vertical rise from the top of the wall plate to the underside of the ridge.
- Measure the horizontal run from the wall plate to the ridge.
- Enter rise and run into the calculator to get pitch, angle, and rafter length.

Safety note

Working on roofs is dangerous, especially on steep pitches or in wet, icy, or windy conditions. Use fall protection, roof jacks, or scaffolding as required, and follow local safety regulations. When in doubt, hire a qualified roofing contractor.

FAQ

What roof pitch is considered flat?

No roof is truly flat; a minimum slope is needed for drainage. Many codes treat roofs below about 2:12 pitch (≈9.5°) as low-slope roofs that require special materials and detailing.

Can I change roofing material without changing pitch?

Each roofing material has a minimum recommended pitch. For example, typical asphalt shingles often require at least 2:12–4:12 depending on manufacturer and underlayment. Always check the product data sheet and local building code before changing materials.

Does roof pitch affect attic space and ventilation?

Yes. Steeper roofs create more attic volume, which can improve storage or allow for habitable loft space. Pitch also affects airflow through soffit and ridge vents, and can influence how easily insulation and air barriers can be installed correctly.

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