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Roof Shingles Calculator: How To Find the Right Amount

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Default Author Icon Written by Angela Bunt Updated 05/02/2024

To properly determine the estimated price for a new roof, you first need to figure out the size of your roof and how many shingles you need to cover it. Fortunately, all this project takes is some careful measuring and a few simple calculations.

In this article, we’ll walk you through finding 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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Roof shingles with garret house on top of the house among a lot of trees. dark asphalt tiles on the roof background
Asphalt Shingle Roofing

The cost of asphalt shingle roof installation can range from $5,994–$9,791.

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Man working on a flat roof
Roof Repair

Typically, the average cost of roof repair ranges between $379 and $1,755

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House With a Metal Roof
Metal Roofing

A new metal roof costs an average of $9,150–$16,743.

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Step 1: Calculate 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 quite simple, 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, and other features that require shingles.

QUICK Tip
Before you start measuring, draw a rough diagram of your roof that includes every plane. You’ll measure the length and width of each plane and write your findings directly on the diagram.

You will need to climb onto your roof to get accurate measurements for each plane. That means you need a sturdy ladder. You will also need a tape measure or laser distance measurer and a notepad. Be sure to take proper safety precautions, such as wearing nonslip footwear and setting up your ladder properly

Note that roof planes may be squares, rectangles, triangles, or trapezoids. The measurements you take and formula you use will vary depending on the shape of your roof.

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.

Square or Rectangular Planes

For a square or rectangular plane, stand at the roof’s peak and measure from the peak down to the eaves; this is the width. Then carefully measure the length from one edge to the other; this is the length. Multiply the length by the width to determine the area.

  • Area = length x width
    • Ex: 20 feet x 10 feet = 200 sq. ft.

Triangular Planes

For triangular planes, measure the base along the roof’s edge and the height from the edge to the triangle’s point.

  • Area = (base x height) / 2
    • Ex: (15 feet base x 10 feet height) / 2 = 150 / 2 = 75 sq. ft.

Trapezoidal Planes

For trapezoids, take one height and two length measurements, one along the bottom edge and one along the peak.

  • Area = [(top edge + bottom edge) x height] / 2
    • Ex: [(8 feet top + 12 feet bottom) x 4 feet height] / 2 = 40 sq. ft.

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.


Step 2: Calculate 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 fall between 4:12 and 9:12.

There are two ways to measure the slope of your roof:

  • From the attic: 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.
  • From the roof: 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.

Roof SlopeMultiplier

3:12

1.031

4:12

1.054

5:12

1.083

6:12

1.118

7:12

1.158

8:12

1.202

9:12

1.250



Step 3: Estimate the Number of Shingles You Need

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.


Choosing the Right Shingles for Your Roof

Roof shingles are available in a number of materials. The most common and least expensive type of shingles are three-tab asphalt shingles, but you can also choose composite, wood, metal, or slate shingles. The best shingle materials for your roof will depend on your climate, budget, and taste.
Asphalt: Asphalt shingles vary in quality, from basic three-tab shingles to premium architectural shingles. They’re very cost-effective and easy to install in nearly all climates, but even the most durable asphalt shingles only last about 30 years.
Composite: Made of a composite of asphalt, fiberglass, and recycled plastics, these shingles can last up to 50 years, but they’re often twice as expensive as asphalt shingles. Their increased toughness makes them better suited to extreme climates than asphalt.
Metal: Metals like steel, copper, and zinc can be formed into shingles. They’re naturally fire-resistant and incredibly durable, with copper roofs lasting up to a century. However, metal roof installation costs are usually quite high, and not everyone likes the modern look of a metal roof.
Slate: Natural stone tiles are even more durable than metal, but slate shingles are generally the most expensive option. They’re also so heavy that roofs typically need to be reinforced before slate shingles can be installed.
Solar: Solar shingles serve the dual purpose of protecting your roof and generating electricity. Though they are more expensive than traditional shingles and less efficient than solar panels, their sleek profile makes them an attractive alternative.
Wood: Wood shakes and shingles provide a classic look and feel. They can be relatively durable, but they require a significant amount of maintenance to protect them from water damage, rot, and pest infestation.

Although asphalt shingles are generally the most popular and affordable option for American homeowners, it’s worth looking into other roofing materials. In the video below, general contractor Tom Silva compares asphalt shingles to three other options: metal roofing, wood shingles, and clay tiles.


How To Hire a Pro

Although measuring is a good do-it-yourself (DIY) roofing project, actually installing a new roof is a job for the pros. Follow these tips to find the right roofing contractor.

  • Make sure each roofer’s license is up-to-date. All states require contractors to carry special licenses to advertise themselves as roofers.
  • Make sure all contractors are bonded and insured to guard against liability.
  • Check each roofing company’s Better Business Bureau (BBB) 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 timelines for both the project and payment.
  • Get quotes from at least three local contractors before making your choice.

Our Conclusion

The first step in estimating the cost of a new shingle roof is figuring out the size of your roof and how many shingles you need. With accurate roof measurements, 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 How Many Shingles You Need for Your Roof

How much will one bundle of shingles cover?

A bundle of traditional asphalt shingles typically covers about 33 square feet. However, other materials may come in smaller bundles. Specifications also vary slightly from one manufacturer to another.

What's the difference between a bundle of shingles and a roofing square?

A bundle of shingles is the physical package you buy, while a roofing square is a unit of measurement. One roofing square equals 100 square feet. You need multiple bundles to cover one roofing square, but the exact number depends on the type of shingles.

How many shingles are in a bundle?

The number of shingles in a bundle varies depending on the size and type of shingle. However, a typical shingle bundle typically contains 15–29 shingles.

My roof has a complex shape. How do I calculate the number of shingles I need?

If your roof has a complex shape, break it down into simpler shapes and measure them separately. Calculate the area of each shape, then add them together to calculate how many shingles you need. Be sure to factor in a higher waste allowance (15–20%) for intricate cuts. 

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