Roof size · squares
Roof squares calculator
Estimate your roof's true surface area, squares, and the bundles and underlayment you'll need — straight from your footprint and pitch.
A roofing square = 100 sq ft. Bundles assume 3 per square; underlayment 4 squares per roll. Confirm with your roofer's measurement before ordering.
Use the squares figure to drive the replacement cost calculator.
From footprint to roof area
Your roof is bigger than the ground it covers, because it slopes. Measure (or estimate) the footprint — the outline of the building including eave overhangs — then multiply by the pitch multiplier to get the real sloped surface. Divide by 100 for squares, the unit roofers actually order and price in.
Why steeper roofs cost more
A 12:12 roof has roughly 40% more surface than its footprint, plus the labor and safety rigging steep work demands. That’s why the cost calculator asks for pitch — and why two homes with the same footprint can have very different roof bills.
Take the squares figure here and drop it into the roof replacement cost calculator to price the job by material.
Frequently asked questions
How do I calculate roof squares?
Multiply your building footprint (the ground area the roof covers, including overhangs) by a pitch multiplier to get the true sloped area, then divide by 100. The calculator does this for you and adds a waste allowance. One square = 100 square feet.
What is the pitch multiplier?
It is the slope length per foot of horizontal run: √(1 + (rise/12)²). A flat roof is 1.0; a common 6:12 pitch is about 1.118; a steep 12:12 is about 1.414. Steeper roofs have more surface than their footprint suggests — which is why they cost more.
How many shingle bundles do I need?
Most asphalt shingles come three bundles to the square, so multiply your squares (including waste) by three and round up. The calculator also estimates underlayment rolls at about four squares per roll. Always confirm against the manufacturer’s coverage and your roofer’s measurement.
How much waste should I add?
A simple gable roof needs around 10%; complex roofs with many hips, valleys, and dormers can need 15–20%. The calculator defaults to 12% and lets you adjust it.
Sources & methodology
- Roofing cost per square / per square foot data — HomeGuide
- National Roofing Contractors Association (NRCA) — roofing standards & material service life
- Roofing material & cost guides — This Old House
- A licensed, insured roofing contractor in your area — the authoritative source for a measured quote and scope
Estimates compiled from the sources above and standard cost models — not professional, insurance, or legal advice, and may not reflect your policy or local prices. See our full methodology and disclaimer.