Roofing Squares Calculator

How to Use the Roofing Squares Calculator

Enter your roof's footprint length and width in feet — that's the size of the building below the roof, not the sloped roof surface itself. Select your roof pitch, add a waste factor for cuts and overlap, and the calculator converts your footprint into actual roof surface area and roofing squares (1 square = 100 sq ft).

How the Calculation Works

A sloped roof has more surface area than its flat footprint because of the pitch. The calculator multiplies your footprint area (length × width) by a pitch multiplier — derived from the roof's rise-over-run using the Pythagorean theorem — to get the true sloped surface area. It then adds your waste percentage on top, and divides by 100 to convert square feet into roofing squares, the standard unit roofers and suppliers use for ordering material.

A few of the pitch multipliers this calculator uses (rise per 12" of run):

• Flat / 1:12 — 1.00×
• 4:12 (common) — 1.083×
• 6:12 — 1.166×
• 12:12 (45°) — 1.474×

Example Calculation

A 40×30 ft footprint at a 4:12 pitch with 10% waste: area = 40 × 30 × 1.083 × 1.10 = 1,429.6 sq ft, or about 14.3 roofing squares.

Frequently Asked Questions

What waste factor should I use?

10% is a common default for a simple gable roof. Roofs with more hips, valleys, dormers, or complex cuts often need 15–20% waste to account for the extra trimming involved.

Is footprint the same as roof area?

No — footprint is the flat building outline, while roof area is the actual sloped surface, which is always larger (except on a flat roof). That's exactly what the pitch multiplier in this calculator corrects for.

How do I find my roof's pitch?

Pitch is expressed as rise over a 12-inch run — a "4:12" roof rises 4 inches for every 12 inches of horizontal run. You can measure it with a level and tape measure in your attic, or check your home's original building plans.