What is a roofing square?

One roofing square equals 100 sq ft of roof surface. Shingle bundles and materials are sold per square, not per square foot.

How do I convert footprint to roof area?

Multiply the horizontal footprint by the pitch multiplier, which is sqrt(1 + (rise/12)^2). A 6/12 pitch has a multiplier of about 1.12.

How many shingle bundles per square?

Three bundles per square for standard three-tab and architectural asphalt shingles. Heavier premium shingles can require four bundles per square.

What is the waste factor for roofing?

Ten percent for simple gable roofs, 15 percent or more for hips, valleys, and cutups. Metal panel roofs waste less because they are cut to length.

Do I need underlayment and drip edge?

Yes. Underlayment goes under the shingles across the entire deck. Drip edge goes at the eaves and rakes to protect the deck edge. Ice and water shield is required in cold climates.

Roofing Material Calculator

Convert roof footprint and pitch into squares, bundles, underlayment, ridge cap, and drip edge. Roof-over jobs and complex hip/valley roofs need higher waste factors.

Roof shape

Footprint

sq ft

Horizontal area under the roof.

Pitch (rise over 12)

6 means 6/12 pitch.

Waste

Material

Edges and ridges

Ridge length

Hip / valley

Eave length

Rake length

Pitch multiplier

1.1x

Actual area

1789 sq ft

Squares (w/ waste)

19.7

Shingle bundles

Underlayment rolls

Ridge cap

50 ft

Starter

84 ft

Drip edge

140 ft

Assumptions

Roof area = footprint x sqrt(1 + (pitch/12)^2).
One square = 100 sq ft; asphalt = 3 bundles per square.
Underlayment covers 4 squares per roll (15 lb felt).
Ridge cap covers ridges plus half of hip/valley length as a planning figure.

Turning footprint and pitch into a bundle order

Roofers quote in squares, where one square equals 100 square feet of actual roof surface. A house footprint alone is not enough; the pitch of the roof stretches the material out. The pitch multiplier is sqrt(1 + (rise/12)^2), so a 6/12 pitch adds about 12 percent to the horizontal area, and a 12/12 pitch adds over 40 percent. Multiply footprint by that factor, divide by 100, and add waste.

Edges, ridges, and starters

A shingle order is more than just field bundles. Starter strip goes along the eaves. Hip and ridge cap covers the ridges and hips. Drip edge is a bent metal profile that goes at eaves and rakes and diverts water off the deck. Underlayment blankets the entire deck under the shingles, and ice-and-water membrane is required at eaves in cold climates.

Why permits and pros matter

Reroofs almost always need a permit and inspection. Steep roofs, complex hips and valleys, and second-story work also compound the safety risk. Use this calculator to size the material bill and sanity check contractor quotes, then hire a licensed roofer for anything beyond a simple shed.

Frequently asked questions

Educational estimates only. Not financial, tax, or legal advice.