Roof Pitch Calculator
Enter the rise and run to calculate roof pitch, angle, slope percentage, and rafter length.
Pitch--
Angle--
Slope--
Rafter Length (per ft run)--
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About Roof Pitch
Roof pitch is the slope of a roof expressed as a ratio of rise (vertical height) to run (horizontal distance). In the US, it's typically given as X:12 — meaning the roof rises X inches for every 12 inches of horizontal run. Pitch affects water drainage, snow load capacity, material choices, and attic space. Common residential pitches range from 4:12 to 9:12. Low-slope roofs (below 2:12) require special waterproofing, while steep pitches (above 9:12) may need additional structural support.
FAQ
What is the most common roof pitch?
The most common residential roof pitch is 4:12 to 6:12. A 4:12 pitch (18.4°) is the minimum for standard asphalt shingles. A 6:12 pitch (26.6°) offers good drainage and attic space. The "ideal" pitch depends on climate, aesthetics, and roofing material.
What roof pitch do I need for shingles?
Most asphalt shingle manufacturers require a minimum of 2:12 pitch, though 4:12 or steeper is recommended for best performance. Between 2:12 and 4:12, additional underlayment is required. Below 2:12, you need a low-slope roofing system like built-up, modified bitumen, or single-ply membrane.
How do I measure roof pitch?
Place a level horizontally with one end touching the roof. Measure 12 inches along the level from that end. Then measure the vertical distance from the 12-inch mark down to the roof surface. That vertical measurement is your rise — giving you rise:12 pitch. A speed square can also read pitch directly.
What is the difference between pitch and slope?
Pitch is expressed as rise:run (e.g., 6:12). Slope is the same concept as a percentage: (rise/run) × 100. A 6:12 pitch = 50% slope. In practice, "pitch" and "slope" are often used interchangeably in roofing, though technically pitch can also refer to rise over the full span (twice the run).