Roof Shingles Calculator

Enter Calculation

Roof Length (ft)

Roof Width / Slope Depth (ft)

Waste Allowance (%)

Enter the total roof surface area dimensions (sum of all slopes). Bundles assume 3 bundles per roofing square (100 sq ft).

Results

Shingle Bundles Needed

40

bundles (3 per square)

Base roof area	1,200 sq ft
Area incl. waste	1,320 sq ft
Roofing squares	13.2 squares

What Is the Roof Shingles Calculator?

This tool estimates how many bundles of asphalt shingles you need to cover a roof. Roofing material is measured in squares, where one square equals 100 square feet of roof surface. Because standard 3-tab shingles are packaged three bundles per square, the calculator converts your roof area into squares and then into bundles, rounding up so you never come up short.

Roof area is the combined surface of all sloped planes, not the building footprint.

How to Use It

Enter the total roof surface area dimensions — the combined length and width (slope depth) of all roof planes. Add a waste allowance (typically 10%) to cover cuts, ridge caps, hips, valleys, and breakage. The calculator returns your base area, the area including waste, the number of roofing squares, and the total bundles to buy.

The Formula Explained

First the surface area is found: \(\text{area} = \text{length} \times \text{width}\). Waste is added: \(\text{roofArea} = \text{area} \times (1 + \text{waste\%})\). Then \(\text{squares} = \text{roofArea} \div 100\), and \(\text{bundles} = \lceil \text{squares} \times 3 \rceil\). The complete relationship is:

$$\text{Bundles} = \left\lceil 3 \times \frac{\text{Length (ft)} \times \text{Width (ft)} \times \left(1 + \frac{\text{Waste (\%)}}{100}\right)}{100} \right\rceil$$

The ceiling function rounds up to the next whole bundle since you cannot buy a partial bundle.

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One roofing square equals 100 sq ft and is typically covered by 3 shingle bundles.

Worked Example

For a roof measuring 40 ft × 30 ft with 10% waste: base area = 1,200 sq ft. With waste:

$$1{,}200 \times 1.10 = 1{,}320 \text{ sq ft}$$

Squares = 1,320 ÷ 100 = 13.2. Bundles:

$$\lceil 13.2 \times 3 \rceil = \lceil 39.6 \rceil = \textbf{40 bundles}$$

FAQ

How many bundles are in a square? Standard 3-tab and many architectural shingles use 3 bundles per square. Some heavier laminated shingles use 4 or 5 — check your product.

Why add a waste percentage? Cutting at edges, hips, valleys, and starter/ridge courses creates offcuts. 10% is typical for simple roofs; complex roofs with many valleys may need 15%.

Is this the same as ground footprint? No — enter the actual sloped roof surface area, which is larger than the building footprint because of the pitch.