You probably know your home’s square footage, but do you know the total square footage of your roof? The measurements are different, and homes with the same floor plans can have different roof areas based on roof pitch and overhangs.

Accurate roof measurements will help you plan your project and buy the correct amount of roofing materials. We’ll show you how to measure and calculate your roof area and discuss the situations when it may be best to hire a roofing professional.

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Why Accurate Roof Measurements Matter

It’s important to figure out your roof’s dimensions to purchase the right number of shingles. You don’t want to make repeated trips to the hardware store for more shingle bundles, nor do you want to end up with extra shingles you can’t return. Accurate measurements will make sure you have enough materials and can plan a realistic timetable for installing shingles to your roof. You’ll also be able to estimate costs and a budget for roof replacement expenses with more precision.

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What To Know Before Measuring

Before climbing onto the roof, gather the right tools and take precautions to reduce your risk of injury.

Tools Required

You may already have the tools you need for this project.

• Calculator
• Ladder
• Measuring tape
• Notepad and pen or pencil

Safety Considerations

There’s always the risk of a fall when working on a roof. Falls are the leading cause of on-the-job injury and death among construction workers, according to 2022 data from the Centers for Disease Control and Prevention (CDC).

Wear closed-toe, slip-resistant shoes. If you plan to do more than just measure, invest in a fall prevention kit approved by the Occupational Safety and Health Administration (OSHA) that includes a harness, heavy-duty rope, and anchoring equipment. We conducted an Amazon search and found that they typically cost $100–$200.

Secure your pen or pencil to yourself or your notepad so it doesn’t roll away. If you drop the pencil, don’t attempt to catch it. Wait until it comes to rest and then retrieve it, repositioning the ladder if necessary.

Over 150,000 people end up in the emergency room each year due to ladder accidents in the U.S. For ladder safety tips, check out the video below with general contractor Tom Silver:

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Step-by-Step Measurement Process

Roof area can be measured by measuring the length and width of each roof plane. A simple gable roof has only two planes, while a hip roof has more. A complex roof with many features will have numerous planes, all of which need to be measured individually.

Step 1: Prepare Beforehand – Walk around your home’s perimeter and draw an overhead view of the roof. This diagram can be a simple outline. It doesn’t need to be to scale but should include every roof plane. That way you can write measurements in the corresponding parts of the diagram. Carefully set up your ladder, angling the base away from the roof’s edge. Put your tape measure, notepad, and writing utensil in your pocket as you climb. You should maintain a three-point grip at all times—this means both feet and one hand on the ladder or both hands and one foot. Move only one hand or one foot at a time.

Step 2: Measure the Roof – Use the measuring tape to measure the length and width of each plane including dormers, eaves, and other shingled roof surfaces. Note the dimensions of features such as chimneys, which will be subtracted from the total square footage. Planes can be squares, rectangles, triangles, or trapezoids. For the height of a triangle, measure from the peak down to the base’s center and then measure the length of the base. For a trapezoid, you’ll need a height measurement and two different length measurements. When measuring from the roof peak down to the edge, stand at the peak and feed your measuring tape down until it reaches the edge. Don’t attempt to start at the edge and work up. To measure roof length parallel to the roof’s peak, stand at one edge and feed your tape measure across to the other edge. Jot down each measurement on your diagram. Note that you don’t need to measure or calculate roof slope, as this isn’t relevant to determining surface area.

Step 3: Calculate the Area – After you’ve taken all necessary measurements, leave the roof before starting calculations. You’ll use your measurements to calculate the square footage of each plane individually and then add those numbers together to come up with the total roof area. Include all surfaces that need shingles. Here are the geometric formulas you’ll need by shape. If math isn’t your strong suit, there are online roofing calculators that can help with this.

• Square or rectangle: Multiply length by height; for example, 10 x 15 = 150 square feet.
• Triangle: Multiply the base by height and divide by two; for example, (12 x 10)/2 = 120/2 = 60 square feet.
• Trapezoid: Add the length of the top to the length of the bottom, multiply by height, and divide by two; for example, [(8 + 12) x 4]/2 = [20×4]/2 = 40 square feet.

Once you’ve determined the total square footage, start calculating the amount of roofing materials you’ll need. Most materials are sold in units called roofing squares, which are 10-by-10-foot (100-square-foot) pieces. To calculate the number of roofing squares you’ll need, divide the total square footage of your roof by 100. For example, if your roof is 2,450 square feet, that’s the equivalent of 24.5 roofing squares.

Regardless of the type of shingles, they’re sold in units called bundles. Each bundle has enough shingles to cover one-third of a roofing square. Thus, for every roofing square, you’ll need three bundles of shingles. Underlayment is typically sold in rolls of either four or 10 squares.

Step 4: Account for Waste – Don’t buy materials based solely on the numbers above or you’ll underestimate the number of bundles. You’ll have to cut some shingles to fit roof angles or to use them as caps or starter shingles. A few three-tab asphalt shingles may arrive cracked or missing granules. If you’re doing the roofing project yourself, have spares on hand in case you make mistakes.

We recommend adding 15% to the number of roofing squares you found earlier. To add 15%, multiply the total number of squares by 1.15. For a roof of 24.5 roofing squares, 29 squares of shingles are required. You’ll need three bundles per square for a total of 87 bundles. Remember to buy enough underlayment, roofing felt, or other materials for 29 roofing squares, too.

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DIY vs. Professional Roof Measurement for Shingles

Putting on a new roof should typically be done by a roofing contractor, but some homeowners may be able to tackle measurements.

DIY Roof Measurement for Shingles

Homeowners should only attempt do-it-yourself (DIY) measurements if they’re confident in their ability to practice ladder and roof safety. You can consider measuring a roof yourself if your home is a single story and its roof is in good shape and not too steep. Measuring to replace a flat roof, for instance, is a relatively easy DIY job. Also, flat roofs are typically less expensive to replace than pitched roofs.

Professional Roof Measurement for Shingles

Consider hiring a professional if you have safety concerns or if your roof is high or steep. Since measuring isn’t a specialty job, you can hire any contractor and pay an hourly labor cost.

Keep in mind that professionals may have safer and more accurate methods, and their estimates often include details on waste percentage and materials beyond shingles.

If your house needs a roof inspection, the measurement can often be done as part of that service or as part of a consultation to upgrade your roof. A roofing contractor will generally fold this fee into the larger cost of roof repair or replacement. Professionals may have safer and more accurate methods, and their estimates often include details on waste percentage and necessary materials beyond just shingles.

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Our Conclusion

Know your roof’s surface area before purchasing high-quality roofing shingles. Measuring a roof is something you can do without extensive DIY skills, but there are safety risks. It’s important to take proper precautions and work carefully when you’re on the roof. Consider leaving this job to experts if you’re already having your roof professionally inspected, cleaned, repaired, or replaced.

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FAQ About Measuring a Roof for Shingles

How do I measure the slope or pitch of my roof?

To measure the slope or pitch of your roof, find its rise and divide that by half the roof’s span. You don’t need to calculate the roof slope to measure for shingles, but you may need it for other reasons. 

Should I measure the roof from the inside or the outside?

You should measure the roof from the outside to get the most accurate measurement of your roof’s surface area.

How do I account for roof features like chimneys and dormers in my measurements?

Measure the surfaces of chimneys and dormers as you would any other roof plane. Dormers and other shingled surfaces should be added to the square footage, and nonshingled surfaces such as chimneys should be subtracted.

What is the waste factor, and how do I calculate it?

The waste factor refers to the amount of extra shingles needed to account for mistakes and imperfect, damaged, or cut shingles. Multiply the number of roofing squares by 1.15 to add an extra 15% for the waste factor.

How many square feet does a bundle of shingles cover?

To determine the number of shingle bundles needed based on roof measurements, take the total roof square footage and divide it by 100 to get the number of roofing squares. Then multiply the number of squares by three for the number of bundles you’ll need.

How many bundles of shingles do I need?

A standard bundle of shingles typically covers about 33 square feet, so you need three bundles for every 100 square feet of roof area. To determine how many bundles you need, calculate your roof’s square footage, divide by 33, and add 10–15% to account for waste.

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