Results update as you type. Round up when ordering.
Based on 3 bundles per square, standard for architectural shingles (e.g. GAF, Owens Corning). Check the wrapper.
Formula checked against manufacturer specs
Rounded up to whole units
Runs in your browser
From footprint to roof area
A sloped roof has more surface than the ground it covers. Multiply the horizontal footprint (including overhangs) by the pitch multiplier √(1 + (rise/12)²). For a 6/12 pitch the multiplier is 1.118; for 12/12 it is 1.414.
Example: 1,500 sq ft footprint at 6/12: 1,500 × 1.118 = 1,677 sq ft. Plus 10% waste = 1,845 sq ft = 18.45 squares → 56 bundles at 3 bundles per square.
What is a “square”?
Roofers measure in squares of 100 sq ft. Most architectural asphalt shingles come 3 bundles per square; some heavier designer lines are 4 or 5—check the wrapper.
Don't forget
Starter strip along eaves and rakes
Ridge cap shingles (measure ridges and hips in linear feet)
Underlayment, drip edge and ice-and-water shield where local code requires
It uses the standard formula shown on this page and rounds bags, boxes and pieces up to whole units. Product sizes vary by brand, so confirm with the label or your supplier before you buy.
Should I buy extra material?
Yes. A 5–10% allowance covers cuts, spills and uneven surfaces; running short mid-job usually costs more than a few leftovers.
Is this calculator free?
Yes. Every PorchMath calculator is free, needs no account and runs entirely in your browser.