Roof Pitch / Slope Calculator

Convert X-in-12, degrees, and percent slope — then multiply plan footprint by the roof-area factor

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Pitch Measurement & Roof Gear

A conversion is only as good as the rise you taped. A rafter square, a magnetic angle gauge, and fall protection are how 6-in-12 leaves the truck as a real number — and how steep work stays legal.

Swanson Rafter Square

Aluminum rafter square for the 12-inch run method: hold the 12" tongue level, read rise on the body. Same X-in-12 the calculator converts.

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Klein Digital Angle Gauge

Magnetic digital angle gauge when you already have degrees from a rafter or a laser. Convert that angle here — do not treat it as percent slope.

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Rooftop Fall-Protection Kit

Guardian Safe-Tie bucket kit. OSHA treats slopes greater than 4-in-12 as steep roofs. Walkability is a decision, not a vibe — see the comparison article.

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Tajima Chalk Line

Snap the 12-inch run on a dry deck when you cannot hold a square against a rafter. Layout mistakes are how percent and degrees get swapped.

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Stair / Square Gauges

Johnson square gauges lock a repeatable rise on a rafter square so every plane is measured from the same reference — not a mixed 6-in-12 and 26° ticket.

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Run the Conversion

Rise, degrees, or percent in — X-in-12, multiplier, and true roof area out.

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How to Use This Roof Pitch Calculator

Pick rise-in-12, degrees, or percent. Type one value. Optionally enter plan footprint (or length × width). Convert. You get X-in-12, degrees, percent, the multiplier, and — if you entered area — actual roof square footage plus a live table of common pitches applied to that same footprint.

multiplier = √(1 + (rise ÷ 12)²) roof sq ft = footprint × multiplier

Worked 6-in-12: atan(6/12) = 26.57°; (6/12)×100 = 50%; √(1+0.25) = 1.118. A 50 × 40 ft plan (2,000 sq ft) becomes 2,236 sq ft of roof on a simple rectangle.

Roof Pitch / Slope Calculator