Roof Pitch Calculator
From 6/12 to degrees, grade, and roof area factor.
Roof Pitch Calculator
Pitch = rise / run; angle = atan(rise / run); multiplier = √(1 + (rise/run)²)
Calculated instantly
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What This Calculator Does
The Roof Pitch Calculator converts a roof’s rise and run into the four numbers trades actually use: pitch as x:12, angle in degrees, percentage grade, and the slope multiplier that turns a building footprint into roof surface area.
How It Works
Pitch is the ratio of vertical rise to horizontal run, normalised to 12 inches of run. The angle is the arctangent of that ratio. Percentage grade multiplies the ratio by 100. The slope multiplier is the hypotenuse of a unit right triangle, so multiplying the footprint by it gives the sloped area.
Example
A roof that rises 6 inches over 12 inches has a 6:12 pitch, an angle of about 26.57°, a 50% grade, and a slope multiplier of 1.118. A 2,000 sq ft footprint therefore has about 2,236 sq ft of roof surface.
Formula
Pitch (x:12) = (rise / run) × 12Angle = atan(rise / run) × 180 / πMultiplier = √(1 + (rise / run)²)Multiply the flat footprint by this to get sloped roof area.
Reading the Results
Roof pitch (x:12)
The standard trade notation: inches of vertical rise for every 12 inches of horizontal run.
Slope multiplier
The factor applied to a flat footprint to get true sloped area. It is why a steep roof needs more shingles than its plan area suggests.
Sources and References
International Residential Code (IRC) — roof covering provisions
Minimum slope depends on the roofing material
The IRC and manufacturer instructions set minimum slopes; this calculator only converts geometry.
References identify the method or data behind this calculator. Where a standard or tariff changes, the current edition applies, and the assumptions stated above take precedence over a remembered figure.
Frequently Asked Questions
What does a 6/12 roof pitch mean?
It rises 6 inches for every 12 inches of horizontal run. That is a 26.57° angle, a 50% grade, and a slope multiplier of about 1.118.
How do I convert roof pitch to degrees?
Divide the rise by the run and take the arctangent, then convert radians to degrees. 6/12 gives atan(0.5) = 26.57°.
What is a roof pitch multiplier used for?
It converts the flat footprint of a building into the actual sloped area of the roof. Multiply the footprint by 1.118 for a 6/12 roof before ordering shingles or underlayment.
What is the minimum roof pitch for shingles?
It depends on the product. Asphalt shingles commonly require at least 2:12 with a double underlayment, and some products require 4:12. Always follow the manufacturer’s installation instructions and local code.