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The cost of a new roof largely depends on your roof’s surface area. It’s bigger than your home’s floor space and is determined by your roof’s pitch, style, and features. No matter what your roof looks like, you can use the following process to take accurate measurements and calculate your roof’s area. We’ll show you how to measure and purchase the right amount of shingles or other roofing materials.
Why Accuracy Matters
Precisely calculating your roof’s total square footage is important for setting your budget and determining how much material you need. The cost of metal roofs, roof shingles, and other materials are primarily determined by square footage, and the more accurate your measurement, the better you’ll be able to plan. You don’t want to end up with too many materials, which wastes money, or too few materials, which wastes time if you need to acquire more.
Important to Know Before You Begin
Before taking roof measurements, prepare for the process by gathering tools and protecting your safety.
You’ll need measuring tape to gauge roof length and height and a ladder to climb up and down. You’ll also need a pad of paper and a pen or pencil to write down each number. After you’ve measured, you’ll need a calculator to complete the process.
Getting precise measurements requires getting up on your roof, which is a substantial safety risk. To protect yourself, use good ladder safety as recommended by the National Safety Council. Climbing up typically means using an extension ladder leaned against the edge of the roof. Always rest the ladder’s base on level ground about three feet away from where the roof overhangs the exterior walls. If the ladder’s top can’t be secured to the roof, have another adult hold the ladder while you’re climbing up or down.
Once on the roof, pay attention to your surroundings to avoid slipping. Wear close-toed shoes that provide a good grip and stay away from any weak spots or loose shingles. You may want to invest in a safety harness, which can be purchased as part of a fall prevention kit that also includes ropes and fasteners. These often cost between $100 and $200. If you intend to do more work on your roof in the future, this is a good investment.
Step-by-Step Measurement Process
Whether you have a simple or complex roof, you can follow these steps to calculate your total roof area and the number of shingles you’ll need to cover it.
Step 1: Preparation
Calculate your roof’s total square footage by measuring the square footage of each plane. Basic gable roofs have two planes, while a hip roof has at least four to six. You’ll also need to measure any dormers, eaves, or other roof surfaces covered with shingles.
The best first step is to draw a basic diagram of your roof so you don’t forget any surfaces. The diagram doesn’t need to be drawn to scale, but it does need to include all the roof’s features that affect the number of necessary shingles. Remember you’ll also need to measure surfaces without shingles, such as chimneys, and subtract them from the total area.
Pick a day with a favorable weather forecast to do your measurements, and set up your ladder in accordance with proper safety practices. Put your tape measure, notepad, and writing utensil in a pocket or bag so you can use both hands on the ladder. If you’re using a fall prevention kit, secure it to the roof as instructed by the manufacturer.
Step 2: Measuring the Roof
Now it’s time to measure the height and width of each plane. To measure height—that is, measuring parallel to the rafters—start at the roof’s peak and advance your tape measure down to the edge. Don’t attempt to sit at or walk down towards the roof’s edge. Measure width parallel to the roof’s peak by staying at one edge and advancing your tape measure across to the other. Write down each measurement as you take it, and ensure you measure every plane and feature.
Many roof planes are squares or rectangles, but not all. Hip roofs are made of triangles and trapezoids. For triangles, make sure you measure the base’s length and the triangle’s height from the point down to the base. For trapezoids, measure the length of each parallel edge—usually the length of the roof’s peak and its edge—as well as the height.
Step 3: Calculating the Area
Next, you’ll use your measurements to calculate your roof’s total square footage. Use the following formulas to determine the surface area of each roof plane separately.
- Square or rectangle: length x height
- Example: 20 feet x 10 feet = 200 square feet
- Triangle: (base x height)/2
- Example: (15 feet x 10 feet)/2 = 150/2 = 75 square feet
- Trapezoid: [(top edge + bottom edge) x height]/ two
- Example: [(8 feet + 12 feet) x 4 feet]/2 = [20 x 4]/2 = 40 square feet
When you’ve calculated the area of each shingled plane, add them together to get the total area. Then, use the same formulas to calculate the area of any features that don’t have shingles and subtract this from the total as follows.
- Total area: Square footage of shingled planes – square footage of unshingled planes = roof square footage
Note that you don’t need to worry about roof slope for these calculations. How much your roof rises plays into how much larger your roof square footage is than your floor space, but you’ll already account for it in measuring the roof’s flat planes. If you’re having difficulty with the calculations, there are plenty of online calculators to help you out.
Step 4: Calculating Roofing Materials
Most roofing materials, including underlayment and three-tab asphalt shingles, are measured in units called roofing squares. A roofing square is simply a 10-by-10-foot area, or 100 square feet. To find the number of roofing squares, divide the total roof square footage by 100. For example a 2,679-square-foot roof requires 26.79 roofing squares of shingles or other materials, rounded up to 27.
Shingles are sold in bundles, and a bundle of shingles will cover about a third of a roofing square. Take the number of roofing squares and multiply it by three to determine the number of bundles you’ll need. For the example above, 27 times 3 equals 81 shingle bundles.
Step 5: Accounting for Waste
No matter what type of shingles you use, you’ll want to have some extras on hand in case of waste. Some will need to be cut into starter shingles or cut to fit around various features on your roof, and you may not always cut them perfectly each time. Additionally, some individual shingles may arrive with defects. Even professional roofers need extra materials, so it’s good practice to add 10% to 15% to the number from Step 4 to account for waste. In the example above, you’d want to buy 89 to 93 shingle bundles in total.
Professional vs. DIY Roof Measurement for Shingles
Roof replacement or repair should always be performed by a professional. However, measuring the roof might be a job homeowners can take on by themselves.
Professional Roof Measurement for Shingles
If you’re not comfortable getting up on your roof, a professional contractor can do the job for you. If you’re already planning to replace or repair your roof, a roofing contractor can take measurements as part of the overall project. This may even be folded into the overall cost of roof repair or replacement.
DIY Roof Measurement for Shingles
As long as you follow proper ladder and roof safety precautions, there’s no reason you can’t measure your own roof. However, we strongly recommend hiring a professional for actual roof installation. They have the tools and training to do the job faster than you can, and many roofing materials must be installed professionally to prevent voiding the warranty. We recommend including labor in the total when considering the cost of shingle roofing.
The first step of planning for roof replacement is measuring your roof so you can get an accurate idea of the amount of materials you’ll need. You can hire a contractor to do this, or you can do it yourself. If you go the do-it-yourself (DIY) route, take care with your safety and your measurements’ accuracy. The more precise you are, the more time- and cost-effective you’ll be.
Roof Measurement for Shingles FAQ
How do I measure the slope or pitch of my roof?
To measure a roof’s pitch, measure the height of your attic and the roof’s span—that is, the distance between the exterior walls, perpendicular to the roof’s peak. Then, divide the height by half of the roof’s span.
Should I measure the roof from the inside or the outside?
You can measure roof slope from inside, but you’ll need to get up on your roof to measure surface area.
How do I account for roof features like chimneys and dormers in my measurements?
You’ll need to find the surface area of every roof feature, adding the area of features that are shingled and subtracting the area of features that aren’t shingled.
What is the waste factor, and how do I calculate it?
The waste factor is the amount of extra shingles you’ll need to account for mistakes or imperfect materials. To calculate a 15% waste factor, multiply the number of roofing squares by 1.15.
How do I determine the number of shingle bundles needed based on my roof measurements?
Once you’ve got the roof square footage, divide it by 100 to find the number of roofing squares. Then, multiply the number of roofing squares by three to get the number of shingle bundles needed to cover it.