What does “6 in 12” mean?

The roof rises 6 inches for every 12 inches of horizontal run. Pitch is quoted over a 12-inch run by convention, so a 6/12 is moderately sloped and a 12/12 is a steep 45°.

How do I measure rise and run?

Hold a level out horizontally from the roof, mark 12 inches along it (the run), and measure straight down from that point to the roof surface (the rise). A pitch finder or a phone app works too.

What's the slope multiplier for?

It converts a flat footprint into actual roof area: footprint × multiplier = roof surface. A 6/12 roof's 1.118 means the surface is about 12% bigger than the ground it covers — see the roof area calculator.

Roof Pitch Calculator

Roof pitch is how steep the roof is — the rise over a run. Enter the rise and run and this gives the pitch in the usual x-in-12 form, plus the angle, the slope multiplier, and the percent grade.

Pitch

6in 12

Angle: 26.6 °
Slope multiplier: 1.118 ×
Percent grade: 50 %

How these numbers are worked out

The formula

Pitch (in 12) = rise ÷ run × 12. Angle = arctan(rise ÷ run), in degrees. Slope multiplier = √(rise² + run²) ÷ run — how much longer the sloped surface is than its run (multiply a footprint by it to get roof area). Percent grade = rise ÷ run × 100.

Constants and sources

Pitch = rise ÷ run × 12; angle = arctan(rise ÷ run); slope multiplier = √(rise² + run²) ÷ run; grade = rise ÷ run × 100. Trigonometry.

How it was checked

Last reviewed June 16, 2026. Before this calculator was published, its formula, constants and worked example were checked in a separate, AI-assisted review that redid the arithmetic and tested the factual claims; the site owner then approved it for publishing. No engineer or tradesperson reviews these pages. Where a figure depends on the product (a density, a coverage rate, a bag size), it is either an input you can change above or a fixed planning value stated on this page, so check it against your product's label or your supplier.

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Worked example

A roof rising 6 inches over 12 inches of run: 6 ÷ 12 × 12 = a 6-in-12 pitch; arctan(0.5) ≈ 26.6°; √(6² + 12²) ÷ 12 ≈ 1.118 ×; 50% grade.

FAQs

What does “6 in 12” mean?: The roof rises 6 inches for every 12 inches of horizontal run. Pitch is quoted over a 12-inch run by convention, so a 6/12 is moderately sloped and a 12/12 is a steep 45°.
How do I measure rise and run?: Hold a level out horizontally from the roof, mark 12 inches along it (the run), and measure straight down from that point to the roof surface (the rise). A pitch finder or a phone app works too.
What's the slope multiplier for?: It converts a flat footprint into actual roof area: footprint × multiplier = roof surface. A 6/12 roof's 1.118 means the surface is about 12% bigger than the ground it covers — see the roof area calculator.