Barn roof material estimator

Gambrel Roof Calculator

Estimate gambrel or barn roof area from building length, lower run, upper run, lower pitch, upper pitch, waste, and material cost. It turns a two-slope roof profile into a practical roof-square takeoff.

Units

Building length (ft)Lower horizontal run (ft)Upper horizontal run (ft)Lower pitch (x/12)Upper pitch (x/12)Waste / cut allowance (%)Cost per roof square or m² ($)

Roof area to order

Roof squares / measured area

Lower and upper slopes

Rough cost

Gambrel roof takeoff is not structural design

This estimates surface area only. Framing design, truss engineering, snow and wind load, hinge points, dormers, valleys, overhangs, ventilation, and code must be verified before building.

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Roof Area Calculator

Use a single-slope or gable-style area takeoff for simpler roofs.

Roof Shingle Calculator

Turn roof squares into bundles and waste.

Roof Pitch Calculator

Convert pitch into angle and slope multiplier.

View all

Gambrel roof formula

Lower slope length = √(lower run² + lower rise²)

Upper slope length = √(upper run² + upper rise²)

Measured area = building length × 2 × (lower slope + upper slope)

Order area = measured area × (1 + waste %)

Sample takeoff

A 30 ft long gambrel roof with 6 ft lower and upper runs, 12/12 lower pitch, 4/12 upper pitch, and 10% waste needs about 978 ft² to order, or 9.8 roof squares.A 9 m long gambrel roof with 1.8 m lower and upper runs, 12/12 lower pitch, 4/12 upper pitch, and 10% waste needs about 88.0 m² to order.

Gambrel Roof Calculator FAQ

How do I calculate gambrel roof area?+

Find the sloped length of the lower and upper roof sections, add them together, multiply by building length and both roof sides, then add waste.Find the sloped length of the lower and upper roof sections, add them together, multiply by building length and both roof sides, then add waste.

Can this size rafters or trusses?+

No. It estimates roof surface area only. Structural gambrel framing needs engineered or code-approved design.No. It estimates roof surface area only. Structural gambrel framing needs engineered or code-approved design.

Should I use roof squares or square metres?+

Use roof squares for imperial roofing suppliers and square metres for metric suppliers unless they quote by another package size.Use roof squares for imperial roofing suppliers and square metres for metric suppliers unless they quote by another package size.