Roof Area Calculator

Calculate roof area from footprint, pitch and overhang — includes waste for shingles or metal.

Roof Area Calculator

Calculate roof area from footprint, pitch and overhang — includes waste for shingles or metal.

Building length (feet)

Building width (feet)

Rise (inches)

Run (inches)

Waste %(%)

Enter values above and click Calculate — results will appear here with the formula explained.

Rafter length = sqrt(rise²+run²) × (width/2 / run); Area one side = rafter × length; Total = both sides × (1+waste)

How does this work?

Roof area is rafter length times building length, times two sides, times waste factor. Rafter length comes from pitch and half-width.

Waste 10% for simple gable, 15% for hip/valley, 5% for standing seam metal.

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Quick Answer

Roof Area Calculator: Calculate roof area from footprint, pitch and overhang — includes waste for shingles or metal. Formula: Rafter length = sqrt(rise²+run²) × (width/2 / run). Example: 40 ft long, 24 ft wide, 6:12 pitch: rafter ≈13.

How to Use This Calculator

1Enter building length and width in feet, rise/run for pitch, and waste.
2See total roof area in square feet and squares (1 square = 100 sq ft).
3Order that many squares of shingles or metal.

Formula Used

Rafter length = sqrt(rise²+run²) × (width/2 / run); Area one side = rafter × length; Total = both sides × (1+waste)

Roof area is rafter length times building length, times two sides, times waste factor. Rafter length comes from pitch and half-width.

Waste 10% for simple gable, 15% for hip/valley, 5% for standing seam metal.

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Worked Example

40 ft long, 24 ft wide, 6:12 pitch: rafter ≈13.42 ft, one side 537 sq ft, total 1,074 sq ft, with 10% waste 1,181 sq ft (11.81 squares).

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Frequently Asked Questions

QWhat is a square?

100 square feet. Roofing is sold by the square. 11.81 squares means 12 squares.

QHip roof?

Hip has 4 sides, not 2. This calculates gable (2 sides). For hip, add ~15% extra.

QInclude overhang?

Yes, rafter includes overhang if entered. Overhang adds ~10% area.

Formula Used

Rafter length = sqrt(rise²+run²) × (width/2 / run); Area one side = rafter × length; Total = both sides × (1+waste)

Roof area is rafter length times building length, times two sides, times waste factor. Rafter length comes from pitch and half-width.

Waste 10% for simple gable, 15% for hip/valley, 5% for standing seam metal.