Roof area calculator

Measure your roof. Plan your materials.

Roof preview

Roof area1,503 sq ft

With 10% waste1,653 sq ft

Roofing squares16.53

Materials estimate

Material	Unit	Quantity
Asphalt shingles	bundles	50
Underlayment	rolls	5
Ridge & hip caps	bundles	2

How it’s calculated

We add the overhang, account for the slope, then apply your waste allowance. Every section is calculated separately.

42.00 × 32.00 × 1.118 = 1,503 sq ft

Formula for Section A. All slopes in a hip section must have the same pitch.

Adjust waste & materials

Waste allowance10%

10% is a starting assumption. Hips, valleys and complex cuts may require more; confirm with your installer.

Measure once. Keep your whole estimate together.

Your sections carry over to the pitch and materials calculators. Print your estimate or export the quantities before leaving. Reloading starts a fresh example.

Roof measurements

Section A: gable, 40.00 × 30.00 ft; overhang 12.0 in; pitch 6.00:12.

Waste: 10%. Planning quantities only; verify before ordering.

01—03 / ROOFING NOTES

How to calculate roof square footage

Measure the horizontal footprint of each roof section at the exterior walls. Add the overhang to both ends of each dimension, then multiply the resulting footprint by the slope factor. This is roof surface area, before material waste.

Roof area calculator Roof pitch calculator Roofing materials calculator

Does roof pitch change the area?

Yes. A 6:12 roof has a slope factor of about 1.118. A 1,000 sq ft horizontal roof footprint therefore covers about 1,118 sq ft of sloped surface.

Can I calculate a hip or an L-shaped roof?

For a rectangular hip roof with equal pitch on every face, the footprint × slope-factor method gives the surface area. For an L shape, add separate non-overlapping sections. Valleys and shared edges require manual adjustment of trim lengths.

Are the diagram dimensions building or roof dimensions?

The form takes building dimensions measured at the exterior walls. The diagram shows roof dimensions after adding the horizontal overhang. The preview is schematic, not a construction drawing.

Why is a roofing square different from square feet?

One roofing square equals 100 square feet. We show the number of squares after your chosen waste allowance. Shingle quantities then round up using the coverage printed on your chosen bundle.