Rafter Length Calculator

Calculate rafter dimensions using rise/run or roof pitch • Live diagram • Unit selection

📏 Rise & Run Method

📐 Pitch Method

Units

Rise & Run

Rise (vertical height)

Run (horizontal distance)

OR: Rafter Length

Rafter Length

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Roof Pitch

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Rise

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Run

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Pitch Angle

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Pitch (ratio)

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Pitch (%)

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Right triangle diagram: Rise (vertical) | Run (horizontal) | Rafter (hypotenuse)

Rafter Formulas (Pythagoras)

Rafter² = Rise² + Run²
Pythagorean theorem

Rafter = √(Rise² + Run²)
Length from rise & run

Pitch (ratio) = Rise / Run
Inches per foot (x:12)

Pitch (%) = (Rise / Run) × 100
Percentage slope

Pitch (deg) = atan(Rise / Run)
Angle in degrees

Rafter = Run × √(pitch² + 1)
Using pitch ratio

Disclaimer: This rafter length calculator provides estimates based on the Pythagorean theorem. Actual rafter dimensions may vary due to overhangs, birdsmouth cuts, ridge board thickness, and local building codes. Always verify all measurements with a licensed structural engineer or qualified contractor before cutting any materials. For informational use only.