To properly budget for a new roof, it’s important to know its size and the amount of shingles needed to cover it. With a little measurement and calculation, this is one home improvement project that homeowners can take on themselves. 

In this article, we’ll show you how to find a roof’s square footage and how this translates into shingle bundles. We’ll also look at the different types of shingles to help you choose the best option.

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Calculating the Area of Your Roof

The first step to determining the number of shingles you need is to get an accurate measurement of the roof’s surface area. Measuring a gable roof with two planes is the simplest, but most roofs have multiple shingled planes. The roof’s square footage includes not just the largest planes or slopes but also any dormers, roof over patios, or other features.

Once you’re on the roof, stand at the peak and use your tape measure or laser distance measure to measure for roof shingles from the peak down to the eaves. Then carefully measure the length from one edge to the other. Note that roof planes may be squares, rectangles, triangles, or trapezoids. 

For triangles, measure the base along the roof’s edge and the height from the edge to the triangle’s point. For trapezoids, take a height and two length measurements, one along the edge and one along the peak. 

Make sure to also measure the dimensions of surfaces that don’t have shingles, such as vents or chimneys.

Once you’ve measured all roof dimensions, calculate the square footage of each plane separately. Use the following formulas depending on the plane’s shape.

• Square or rectangle: length times height
  • Ex: 20’ length x 10’ height = 200 sq. ft.
• Triangle: base times height divided by two
  • Ex: (15’ base x 10’ height)/2 = 150/2 = 75 sq. ft.
• Trapezoid: edge 1 plus edge 2 times height divided by two
  • Ex: [(8’ top + 12’ bottom) x 4’ height]/2 = [20×4]/2 = 40 sq. ft.

Once you’ve calculated all the planes separately, add them together to find the roof’s total square footage. Subtract out the surface area of chimneys, vents, and other non-shingled features. Note that roof area is often expressed in terms of roofing squares, which are measures of 100 square feet. To determine the number of squares, divide the total square footage by 100. This number will help you purchase shingles as well as other roofing materials, such as underlayment.

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Calculating the Pitch of Your Roof

Roof pitch plays a much smaller role in determining shingle count than total roof area, but steep roofs will require slightly more shingles. Even a so-called flat roof usually has some slope. Pitch is measured in vertical rise over horizontal run—in other words, how many inches it rises for every horizontal foot of roof length. For example, 3:12 roofs rise 3 inches for every foot (12 inches) and are considered low-slope roofs. Alternatively, 6:12 roofs rise 6 inches for every foot and are considered high-slope. Most residential roofs are between 4:12 and 9:12.

If you have an attic, you can measure roof slope from the inside. Measure the attic’s height from the floor to the highest ceiling joist. Then measure the roof’s span, or the distance between the exterior walls that are perpendicular to the roof peak, and divide by 2. The height over the divided span is the pitch. 

Alternatively, you can get on your roof and use a tape measure and a level that’s at least 12 inches long. Touch one end of the level to the roof’s surface and adjust the level until it’s perfectly flat. Then measure the height from the roof’s surface to the level’s 12-inch mark. This will be the roof’s rise, and 12 is the run.

Use the slope to determine the pitch multiplier. You’ll multiply your roof’s square footage by this number to adjust for extra shingles required by steepness. For example, a 1,764-square-foot roof with a 6:12 slope should be multiplied by 1.118 for a total of 1,972.

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Estimating the Number of Shingles You Need

Regardless of the type of shingle material, shingles come in bundles that cover about 33 square feet of roof surface. That means you’ll need three shingle bundles for every roofing square—that is, every 100 square feet. Multiply the number of roofing squares by three to estimate the number of bundles you need. For example, a roof of 1,764 square feet is composed of 17.64 roofing squares. Supposing it has a 6:12 slope, this number should be adjusted to 1,972, or 19.72 squares, rounded up to 20. To cover this roof, you’d need 20 x 3 = 60 bundles of shingles.

You also need to account for overage when calculating the amount of materials to buy. Shingles often need to be cut to fit around vents or pipes or turned into ridge caps, so include an extra 15% for wastage. Multiply the number of bundles by 1.15 to get your new total. For example, 60 x 1.15 is 69, so to account for overage, you should buy 69 bundles of shingles to cover a roof of 1,764 square feet. If you’re still having trouble, an online shingle calculator can help you with the math.

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How To Hire a Pro

Although measuring a roof and calculating the amount of shingles is a good do-it-yourself (DIY) roofing project, actually installing a new roof is a job for the pros. Here’s how to find the right roofing contractor.

• All states require contractors to carry special licenses to advertise themselves as roofers. Make sure each roofer’s license is up-to-date.
• Make sure all contractors are bonded and insured to guard against liability.
• Check each roofing company’s Better Business Bureau webpage to learn how long they’ve been in business, how well they’re rated, and how they deal with customer complaints.
• Ask for references and check customer review sites such as Trustpilot and Google Reviews.
• Inquire about warranties on both materials and workmanship.
• Make sure you understand time lines for both the project and payment.
• Get quotes from at least three local contractors before making your choice.

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Our Conclusion

The first step in determining shingle roof pricing is figuring out how many shingles it takes to cover your roof. With an accurate roof measurement, you can use a roofing calculator or a few simple formulas to determine how many squares of shingles you’ll need. This will help you set your budget accurately and prepare for potential overage costs.

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FAQ About Calculating the Number of Shingles for Your Roof

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