BuildCalcs

Roofing Calculator — Squares and Shingle Bundles

By BuildCalcs · Updated

Enter the footprint of your house and the roof pitch. This calculator adjusts for the slope, then gives you the roof area, the number of roofing squares, and how many bundles of shingles to buy.

Roofing squares14.76 squares
Shingle bundles45 bundles
Roof area (with waste)1,475.8 sq ft
Slope factor1.118 ×

How to use this calculator

  1. Measure the length and width of the building footprint the roof covers, in feet.
  2. Choose the roof pitch — the rise in inches for every 12 inches of horizontal run. 6 in 12 is the most common.
  3. Pick 10% waste for a simple gable roof, or 15% if it has many hips and valleys.
  4. Buy shingles by the bundle; about 3 bundles cover one roofing square (100 sq ft).

The formula

A sloped roof is larger than the footprint it covers, so we scale the footprint by a slope factor.

Slope factor = √(1 + (rise ÷ 12)²). For a 6-in-12 pitch that is √(1 + 0.25) ≈ 1.118.

Roof area = footprint area × slope factor. Add 10–15% waste.

Roofing squares = roof area ÷ 100. Bundles = squares × 3 (standard 3-tab / architectural shingles), rounded up.

Worked example

A 40 ft × 30 ft footprint, 6-in-12 pitch, 10% waste.

  1. Footprint = 40 × 30 = 1,200 sq ft
  2. Slope factor (6/12) = √(1 + 0.25) ≈ 1.118
  3. Roof area = 1,200 × 1.118 ≈ 1,342 sq ft
  4. With 10% waste ≈ 1,476 sq ft → 14.76 squares
  5. Bundles = 14.76 × 3 ≈ 45 bundles

This roof is about 14.8 squares — roughly 45 bundles of shingles with 10% waste.

Frequently asked questions

What is a roofing square?

A roofing square is 100 square feet of roof area. Roofers measure and price work by the square, and one square typically takes 3 bundles of shingles.

How many bundles of shingles do I need?

Plan on 3 bundles per roofing square. Divide your total roof area (with waste) by 100 to get squares, then multiply by 3 and round up.

How does roof pitch change the amount?

Steeper roofs have more surface area than their footprint. A 6-in-12 pitch adds about 12%, a 12-in-12 pitch adds about 41% over the flat footprint area.

How much waste should I add for shingles?

Add 10% for a straightforward gable roof and 15% for complex roofs with many hips, valleys, and dormers, which require more cuts.

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