Roof pitch is the slope of a roof expressed as a ratio of vertical rise to horizontal run. In the US, it's typically written as X:12 — meaning the roof rises X inches for every 12 inches of horizontal run.
Why Pitch Matters
Material quantities: A steeper pitch means more actual roof area than plan area. Use the pitch multiplier to convert your blueprint sq ft to actual roofing sq ft.
Rafter length: The steeper the pitch, the longer the rafters needed — critical for ordering lumber.
Shingle type: Low-slope roofs (below 2/12) require special underlayments and materials.
Labor cost: Steep roofs (above 8/12) are significantly more dangerous and expensive to work on.
Common Roof Pitches by Application
2/12 – 3/12: Low slope — flat-style roofs, requires special shingles or membrane
4/12 – 5/12: Common residential — easy to walk, standard shingles
6/12 – 8/12: Moderate — most common in the US, good drainage
9/12 – 12/12: Steep — dramatic look, harder to work on, great for snow shedding
Above 12/12: Very steep — requires safety equipment, specialty contractors
The Pitch Multiplier Explained
If your floor plan shows a 20×40 ft footprint (800 sq ft), and your roof has a 6/12 pitch (multiplier 1.118), the actual roof surface area is 800 × 1.118 = 894 sq ft. This is what you order materials for.
Got your pitch? Calculate your shingles.
Take these numbers into the Roofing Squares Calculator to get your bundle and square count.