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Roofing Calculator: Shingles, Squares and Bundles

Estimate roofing squares and shingle bundles from your roof's footprint and pitch. Add waste, ridge cap and underlayment, and price it yourself.

How to use the Roofing Calculator

  1. Measure the footprint of each roof section from the ground, out to the edge of the eaves. Enter its length, width and pitch.
  2. Add a section for each part of the roof that has a different pitch.
  3. Set the waste percent and the bundles per square from your shingle label.
  4. Read the squares and the number of bundles to buy. Add a price per bundle to see the shingle cost.

How the roofing calculator works

A roof slopes, so its surface is larger than the footprint of the house under it. The calculator multiplies each section's footprint by a slope multiplier, which is the square root of 1 plus (rise divided by 12) squared. This works for gable and hip roofs alike, as long as the section has one pitch.

Pitch Slope multiplier Roof area for a 1,000 sq ft footprint
2/12 1.014 1,014 sq ft
3/12 1.031 1,031 sq ft
4/12 1.054 1,054 sq ft
5/12 1.083 1,083 sq ft
6/12 1.118 1,118 sq ft
7/12 1.158 1,158 sq ft
8/12 1.202 1,202 sq ft
9/12 1.250 1,250 sq ft
10/12 1.302 1,302 sq ft
12/12 1.414 1,414 sq ft

A roofing square is 100 square feet of roof. Divide the roof area by 100 to get squares, add your waste allowance, then multiply by the bundles per square (3 is common) and round up to whole bundles.

Worked example

A 40 by 30 foot footprint with a 6/12 pitch:

  • Footprint: 1,200 sq ft
  • Roof area: 1,200 x 1.118 = about 1,342 sq ft, or 13.4 squares
  • With 10 percent waste: 14.8 squares
  • Bundles at 3 per square: 44.3, rounded up to 45 bundles

How much waste to add

Waste covers cuts along edges, hips, valleys and ridges, and mistakes. Common guidance is about 10 percent for a simple gable roof and 15 percent or more when the roof has hips, valleys, dormers or many cuts. Enter your own figure if a roofer has given you one.

Ridge cap and underlayment

Shingle coverage is on the package, so enter it and the calculator does the rounding. Under Ridge cap and underlayment, enter the total length of your ridges and hips and the feet one bundle of ridge cap covers, and the square feet one roll of underlayment covers. The tool does not guess these numbers because they differ by product.

What this estimate leaves out

It covers shingles, ridge cap and underlayment quantities only. It does not include tear-off, labor, flashing, vents, drip edge or disposal, and it assumes each section has one pitch. Use it to compare quotes and plan a budget, not as a bid.

Measure safely

Measure from the ground and stay off wet or steep roofs. If you suspect damage, see signs your roof may need repair or replacement. If a ceiling stain showed up after rain, here is how to trace it. In cold climates, ice dams can also send water under shingles.

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Planning other work? Try the fence cost calculator, the flooring calculator or the wallpaper calculator.

Frequently asked questions

How do I calculate roofing squares?

Multiply the footprint area of the roof by the slope multiplier for its pitch, then divide by 100. A roofing square is 100 square feet of roof. A 40 by 30 foot footprint at 6/12 is 1,200 times 1.118, or about 1,342 square feet, which is 13.4 squares before waste.

How many bundles of shingles are in a square?

Three bundles usually cover one square. Some heavier or specialty shingles need four or more, so check the coverage printed on the package and change the bundles per square in the calculator.

How much waste should I add for roofing?

Sources commonly suggest about 10 percent for a simple gable roof and 15 percent or more for roofs with hips, valleys, dormers or many cuts. A roofer can give a better figure for your roof.

Should I include the roof overhang?

Yes. Eaves and gable edges often extend 12 to 24 inches past the walls. Measure to the outer edge of the roof, not the house walls, or the area will come out too small.

How do I measure a roof without climbing on it?

Measure the footprint from the ground with a tape measure or a measuring wheel, out to the edge of the eaves, then multiply by the pitch factor. Estimate the pitch from a photo or a pitch gauge. Leave anything that needs walking on the roof to a roofer.

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