Free roofing square calculator.
This free roofing square calculator converts a building footprint and roof pitch into the actual sloped surface area, then expresses it as roofing squares (1 square = 100 ft²). Add waste for hip roofs, valleys, and cut-up sections. Imperial or Metric.
Roof area
Want this measured straight from your PDF instead? BidScreen XL adds the same math to Microsoft Excel — trace the drawing, the quantity lands as a live cell.
Plan area × pitch multiplier.
The roof's plan area is the footprint of the building when viewed from straight above. A 40 × 30 ft house has a 1,200 ft² plan area. But the actual roof is pitched, so its surface area is larger than the footprint.
The pitch multiplier is the secant of the slope angle, computed as sqrt(1 + (rise/12)²). For a 6/12 pitch: sqrt(1 + 0.25) ≈ 1.118. A 12/12 (45°) pitch is sqrt(2) ≈ 1.414. Memorise the common ones — 4/12 ≈ 1.054, 6/12 ≈ 1.118, 8/12 ≈ 1.202, 12/12 ≈ 1.414.
Roofing material is sold by the square — 100 ft² of coverage. Multiply your plan area by the pitch multiplier, add a waste percentage, divide by 100, and you have the number of squares to order.
Frequently asked
What is a roofing square?
One roofing square equals 100 square feet of roof surface area. Roofing materials — shingles, underlayment, ice and water shield — are priced and packaged by the square. A 2,500 ft² roof is 25 squares.
How do I find the pitch multiplier?
Pitch is rise per 12-inch run. A 6/12 pitch rises 6 inches over 12 inches of horizontal run. The pitch multiplier is sqrt(1 + (rise/12)²): 6/12 ≈ 1.118, 8/12 ≈ 1.202, 12/12 ≈ 1.414. Multiply your roof's plan area (footprint) by the multiplier to get the actual sloped surface area.
Why is my roof bigger than the footprint?
Because it's pitched. A flat (0/12) roof equals its footprint. A 6/12 roof has 11.8% more surface area than the footprint. A 12/12 roof has 41.4% more. The steeper the pitch, the more material you need.
How much waste should I add for shingles?
10% for a simple gable. 12-15% for hip roofs (more cuts at hips and valleys). 15-20% for cut-up roofs with multiple dormers, valleys, and ridges. Architectural shingles need less waste than 3-tab.
Does this account for hips, valleys, and ridges?
Not directly. The pitch multiplier is exact for the planar surface area; the waste percentage covers the extra material consumed by hips and valleys. For a heavily complex roof, BidScreen XL traces each roof plane on the drawing and gives you per-plane square footage to bid each section accurately.
BidScreen XL traces each roof plane separately.
For complex roofs with multiple planes, hips, and valleys, BidScreen XL lets you trace each plane on the roof plan with its own pitch and gives you per-plane square footage, ready to drop into your Excel bid as live formulas.