How to measure a roof for shingles: A complete guide

Key points

• You can roughly estimate your roof area from the ground to stay safe.

• Hire a professional to avoid excess material waste and potential insurance claims.

• Bundles of different shingle types contain different numbers of shingles, but they all cover the same area.

Taking accurate roof measurements can save you time and money. Overestimating the number of shingles you need could leave you with unused shingles when you’re finished, while underestimating how many shingles you need will require additional trips to the store.

“Running out of roofing material while on the job can [also] mean mismatched colors and batch attributes,” said Korey Gregory, superintendent at ASAP Restoration, a home renovation company in Tempe, Arizona.

Measuring a roof yourself is possible, but it’s not advised. “I strongly recommend that customers hire a professional for their roofing needs,” advised Chris Hock, owner of Earth Saving Solutions, a full-service home renovation company in Denver. 

“[Roof work] involves many intricate details and safety considerations. Professionals are equipped to handle these complexities, which can ultimately save homeowners money by reducing waste and preventing costly mistakes,” he said.

It’s possible to get a rough roof size estimate from the ground. Measure the length and width of your home, add 4 feet to each to account for overhangs, multiply the figures and add 10% to account for waste.

Understanding how factors such as roof pitch and waste factor is a good place to start for a DIY roof replacement to save time and money and make sure all of your shingles match.

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How many shingles does an average roof need?

The number of shingles a roof requires varies based on roof pitch, home size and special considerations. For instance, you’ll need additional roofing material to cover dormers and fit around vent pipes and chimneys.

“We might expect the roof size of a [typical] 2,000-square-foot ranch home to land within 2,200 to 3,000 square feet,” explained Hock. “This estimate includes considerations for typical overhangs and the pitch of the roof.

“To translate this into the language of roofing professionals, we would express this area in terms of ‘squares,’ a term used to denote a 10-by-10-foot section of roofing, equivalent to 100 square feet. Thus, the roof of our hypothetical home could require between 22 and 30 squares of roofing material, factoring in our waste percentage,” he continued.

How do you calculate how many shingles your roof needs?

Getting up on a sloped roof is dangerous, so the easiest way to measure your roof is to get an estimated square footage from the ground. You’ll need to measure the width and the length of your house to get started. However, this won’t account for roof pitch, so remember that your numbers could vary.

“[Assume] a standard roof pitch of 4:12 rise over run (which means the roof rises 4 inches for every 12 inches of horizontal run) and a typical overhang of around 1 to 2 feet on each side,” said Gregory. “If the home is a square with sides of 50 feet [and 2-foot overhangs]:

Width = 50 feet + 2 feet + 2 feet = 54 feet

Length = 50 feet + 2 feet + 2 feet = 54 feet

Roof area = 54 feet x 54 feet = 2,916 square feet

Add an additional 10% to this total for waste and off-cuts.”

Shingles are sold in bundles and not individually, so you’ll need to divide your total roof square footage by the square footage on your chosen package of shingles to calculate the number of bundles you should buy.

Alternatively, you can take physical measurements for a more accurate number. To accomplish that safely and efficiently, you’ll need the following tools:

• Ladder
• Measuring tape
• Notepad
• Pen/pencil

You’ll also need to plan out your measurements to make it easy to calculate the total area of the roof later. Break up your roof into rectangular, triangular and trapezoidal sections to make it easier to calculate the area. You can use the following formulas to calculate the area of each section:

• Area of a square or rectangle: length x width
• Area of a triangle: base x height / 2
• Area of a trapezoid: (top length + bottom length) x height / 2

You don’t technically need to use trapezoids since you can break up a trapezoid into a square and two triangles, but knowing how to calculate the area of a trapezoid can speed up the process since you’ll take fewer measurements.

Plan your measurements

It’s easy to lose track of the areas you’ve already measured if you don’t have a plan. Take a few minutes to walk around the outside of your home with a pen and pad to diagram the areas of your roof. This can be a simple sketch, but make it large enough to write the dimensions inside each section.

Once the basic sketch is done, divide the roof into squares, rectangles, triangles and trapezoids you’ll measure once you’re up on the roof. Mark out the specific measurements you want to take so you can fill them in quickly while you work.

You need to measure all of the surfaces to be covered by shingles. That includes the main roof planes, tops of dormers and eaves. For simple roof types, such as a gable roof, you only need to measure the length and width of each plane. Hip roofs and other complex roof setups require more measurements since they’re made up of more shapes.

Measure your roof

Take some safety precautions before you break out the ladder and head up on the roof. We recommend measuring your roof with the help of a partner. Your partner can hold the ladder to make it safer to get on and off the roof. Position your ladder on stable ground, even if you have a partner hold it for you.

Measure each of the sections you planned out during your preparation. When you’re finished, pause to ensure you didn’t miss any measurements. If you wait until you’re on the ground to check, you risk taking another trip up the ladder.

Calculate your roof area

With your measurements in hand, it’s time to do a little bit of math. Calculate the area of each of the sections you marked out in the planning step. Write the area inside the sketch of the section on the same piece of paper to keep things organized.

Once you calculate the area of each section, you can add up the values to get your total roof area.

If you measured each section in feet, the area numbers are in square feet. It can be helpful to convert this square footage to squares, which is the unit most roofers use to estimate how many shingles they need. One square is equal to 100 square feet, so converting square feet to squares is as easy as dividing the area of your roof by 100. Here are a few examples:

• 1,700 square feet = 17 squares
• 2,000 square feet = 20 squares
• 2,500 square feet = 25 squares
• 3,000 square feet = 30 squares

Unfortunately, you can’t purchase shingles by the square. Instead, most roofing supply companies sell shingles by the bundle. No matter what type of shingles you’re buying, one shingle bundle equals one-third of a square or 33.33 square feet. You’ll need three times as many bundles as the number of roofing squares you need.

Here are some examples of the bare minimum number of bundles you need for each number of squares we calculated above:

• 17 squares = 51 bundles
• 20 squares = 60 bundles
• 25 squares = 75 bundles
• 30 squares = 90 bundles

However, it’s wise to buy more shingles than you need. Here’s why.

Calculate roof waste factor

Shingles overlap, and you must account for cutting shingles to fit around your chimney, vents, skylights and overhangs. Fitting shingles to the edge of the roof and accounting for the extra overlap around ridge caps requires more cutting and more waste. 

Most roofers account for an additional 10% above your roof square footage when estimating how many shingles you need.

“For the DIYer doing this for the first time, you might want to add a little more than 10% to be safe,” said Gregory. This will help ensure you don’t make unnecessary trips to the home improvement store and can also avoid color mismatches from different batches from the manufacturer.

Your roof type can also affect the proper waste factor for your application. “If it’s a gable roof, waste could be 10%, but a hip and ridge roof could be 20%,” explained Hock.

Play it safe and get 15%–20% more than the area calculation says you need.

The table below shows how many extra bundles you need, assuming 10% and 15% waste factors for several roof sizes.

No Waste Factor	10% Waste Factor	15% Waste Factor
51 bundles (1,700 square feet)	56 bundles	59 bundles
60 bundles (2,000 square feet)	66 bundles	69 bundles
75 bundles (2,500 square feet)	83 bundles	87 bundles
90 bundles (3,000 square feet)	99 bundles	104 bundles

Roofing terminology

What is a shingle bundle?

What is a roofing square?

A shingle bundle is a package of shingles that covers 33.33 square feet, or one-third of a square. This number is chosen because it’s equal to the size of the pieces of plywood used to construct your roof deck. Selling shingles in bundles makes it easy for roofers to figure out how many bundles they need to cover a roof. The amount of shingles in a bundle varies based on the type of shingle, but the area covered is always 33.33 square feet.

A roofing square is a 10-foot by 10-foot area equal to 100 square feet of roof surface. Roofing contractors use roofing squares to talk about roof sizes, where the number of squares of shingles you need equals your roof’s size divided by 100. For example, if you have an average-sized 2,000-square-foot roof, you need 2,000/100 = 20 squares worth of shingles to cover your roof.

What’s next?

With roof measurements in hand, you have two options for moving forward:

• Purchase your calculated amount of shingles and proceed with a DIY roof replacement. Those measurements are also helpful for determining the amount of other roofing materials you need, such as underlayment, drip edges and flashing.
• Use your measurements to purchase materials and have a professional roofing company handle the installation. This option can help you avoid markups for materials while benefiting from the knowledge and expertise of professional roofers.

It’s important to carefully consider whether you want to take on a DIY roof replacement, especially if you’re inexperienced and lack the proper safety equipment. 

“Doing [roof] work poorly yourself may even undermine any potential insurance claims you may make in the future if the DIY repair [or replacement] was the cause of loss or related to it,” said Korey. Reach out to a pro to keep yourself safe and avoid problems down the road.