- Calculating a roof’s area requires a tape measure and a piece of paper.
- Break the roof into planes and shapes, then measure them like regular two-dimensional objects.
- A bundle of shingles covers 33 square feet. To estimate shingle cost, take the area of the roof, factor in 10% to 15% for waste, and divide that by 33. Take the product and multiply it by the cost of a bundle of shingles.
As a roofing professional, I’ve had a lot of experience measuring and estimating costs for roofing projects. One of the most important parts of the process is offering an accurate estimation, which ensures that the client has the correct information and knows what costs to expect. Proper estimation allows the project to go smoothly — the right amount of roofing materials arrive on time, clients are prepared for the expenses, and workers only have to worry about completing the work quickly and efficiently.
In this guide, I’ll explain how to calculate the area of a shingle roof. Once you can measure your roof, you can get a good idea of what a new roof will cost, even before the roofers show up. We also suggest you read our article on how to plan for a roof replacement.
Check out my recommended roofing companies if you’re ready for that new roof today:
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Specialized metal shingles
Service area spans dozens of states
Provides first-time roof installation & military discounts
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Thousands of 5-star reviews
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Top-quality shingles
Provides windows & solar system services
Quick, thorough installations
How Do You Measure Your Roof for Shingles?
Measuring a roof is a straightforward process. If you remember how to calculate area (length x width), you’re all set. The rest is taking accurate measurements, which requires just a ladder, a tape measure, and a piece of paper.
Before we proceed, a word about safety: Roofs are dangerous. Falls, even from short heights can result in permanent injury or disability. So, be careful when accessing your roof. Make sure you know proper ladder safety and how to walk a roof before starting any measurements.
The Basic Calculation for Roof Area
To calculate the roof area, start by breaking up the roof into planes. Imagine the two slopes on each side of a roof — each of those can be considered a roof plane. As roofers, we like those flat surfaces (planes) because we can easily calculate their area by multiplying the rake by the length. Complete these three easy steps to calculate your roof’s area:
1. Measure the Rake
Rake has a few different uses as a term, but in this case, it’s the measurement from the ridge of the roof to the gutters or edge of the roof. That measurement is a right angle off the ridge, so if you imagine the ridge as a line, the measurement is 90 degrees off that and directly down the roof pitch to the roof’s edge (check out standard roof pitch).
Measuring down to the roof’s edge can be risky, so have a partner on the ground stand on a ladder and hold the tape on the edge while you walk to the peak.
2. Measure the Length
Next, measure the length. That’s as easy as it sounds: Measure along the roof’s edge. For a simple open gable roof, the roof length is the measurement along the roof’s low edge that runs the length of the house (the edge that has gutters.)
3. Do the Math
To get the roof area, multiply the rake by the length. If an open gable roof has a rake measurement of 15 feet and a length measurement of 50 feet, the roof has an area of 750 feet. Remember, though, that’s the area of just one plane of your roof. We have to account for the other side, too. In this example, if the open gable roof has equal sides, it means you’ll have to double that number: 750 feet x 2 makes for a total of 1,500 feet.
For a simple gable roof, you can also just measure across the whole width of the roof, then take the length and calculate the area.
Calculating the Area of a Roof With a Hip
You may see what I’m getting at here. For a simple open gable roof, you essentially have two rectangles leaning against each other, so you can calculate the area of each rectangle without having to consider pitches or angles using the easy multiplication of length x width.
But what about hips? A roof with hips doesn’t have nice 90-degree rectangular sides. In order to calculate the area, you have two options:
Ignore the Hip
The first option: You don’t measure the hip. You still calculate the rake times the length, and even though that calculation is over the actual area of the hipped side, the difference will be washed out by the waste factor. (Shingling edges, valleys, and hips always mean cutting and wasting parts of shingles, which means you have to order more shingles than the exact square footage of the roof. As such, we can compensate for our short-cut calculation by adjusting the waste factor down.)
A hip roof will also always leave a triangular section across the short side of the house. Calculate this rake x length and chalk the rest up to waste, too. If that leaves you with extra shingles, that’s great. Having a few bundles of roof shingles left over means you can store them in case you ever need to replace damaged shingles or repair the roof.
Calculate It Using Sections
The second option: You calculate it. This is a little trickier, but it’s not too hard. Find the point where the hip diverges from the ridge and draw an imaginary line straight down the slope of the roof to the gutters. Now, we’ve created a triangle section and a rectangular section. Calculate the rectangle section length x width and calculate the triangle section length x width / 2.
For the triangular section across the short side of the house, measure from the peak down to the edge of the roof, then across the entire base and divide by two. That’s the area of that section. Add all your numbers up and that’s the exact measurement of the area of your roof.
Calculating the Area of Complex Roofs
As you can see from the aforementioned sections, the main idea for calculating roof area is breaking the roof down into smaller, flat shapes that you can measure, calculate the area, and add up the totals. Professional roofers use this core method to calculate the area of any roof, no matter how complex.
The other thing to remember is that roofs are made up of basic shapes. A roof is never more than surfaces that can be broken down into triangles and rectangles.
Chalk is your friend when doing roof measurements. It can help you break the roof down into those basic shapes and mark out lines of roof measurements to calculate it. The chalk won’t harm the roof and will wash away when it rains, so draw all you want. You can never mark and annotate too much.
My preferred strategy is to mark out the big rectangles first, then add those up. After that, I calculate all the smaller triangle sections. Finally, I add the measurements of the rectangles and triangles together to get an exact measurement of the roof’s surface area.
Most of the triangles in a roof are right triangles or isosceles triangles, so they should be relatively easy to work with. It helps to remember that an isosceles triangle always bisects down the middle into two right triangles.
Calculating the Waste Factor of Your Roof
As I mentioned, there’s always an amount of waste created when shingling, which means we need to order more shingles than the exact coverage amount. This waste factor is between 10% and 20%, though I only expect to see 20% on a very complex, non-standard roof. For standard roofs on typical house styles (ranches, split-levels, and colonials), 10% to 15% waste is my usual estimate.
If you followed my previous strategy for hips, plan to take this waste factor into consideration. We took a shortcut with the measuring process and chalked the difference up to waste, so we need to account for that. Adjusting down 2% to 3% is adequate for these types of roofs.
Remember, having extra shingles when you’re done isn’t bad at all. It can save you significant money and time down the road if you need repairs and they don’t make your shingles anymore.
Read also: Metal Roof Recycling for Sustainability
I suggest keeping three to five bundles of shingles on hand in case you need them for future repairs.
4.1
Specialized metal shingles
Service area spans dozens of states
Provides first-time roof installation & military discounts
3.9
Thousands of 5-star reviews
Phone, email, & text consultations
Factory-trained installers
3.7
Top-quality shingles
Provides windows & solar system services
Quick, thorough installations
What Do You Need To Measure a Roof for Shingles?
You only need a few tools to measure a roof, most of which you probably already have. If you don’t, all the tools listed below are cheap and available at any big box store. Here’s what you need:
Tape Measure
In this case, a metal retractable tape measure isn’t ideal, as it’s not long enough. You can certainly make do with one if it’s all you’ve got, but you’ll need to mark the spot where your tape runs out and reset it to continue the measurement.
The best tape measure is a 100-foot tape measure. Unlike the metal retractable tape measure we’re all accustomed to, it’s a cloth tape on a spool with a crank. These types of measuring tapes can be a bit cumbersome but work well for long measurements such as these.
Ladder
You’ll need to access your roof, so having a suitable ladder is essential. For a single-story roof, a 10-foot ladder is best. Using an 8-foot ladder is technically possible, but I strongly advise against it. Going up is easy, but getting down can be risky.
In general, a ladder should be a few feet taller than whatever you’re climbing. Since the base of a roof is 8 feet (at least), you’ll be at the very top of your ladder, making it unstable and unsafe.
Ladders can be expensive, so I wouldn’t purchase one just to measure a roof. If you don’t have one or one that’s tall enough, ask friends or family if they have one you could borrow.
Pen and paper
Estimating a roof’s material requires numerous measurements and some math, so having something to keep notes on and do arithmetic is essential. Alternatively, you can use a notes app on your phone — and your phone also doubles as a calculator, too.
How Do You Estimate the Cost of Shingles for Your Roof?
The first step is to figure out what type of shingles you want. Numerous manufacturers make shingles in various styles and colors. You can find them at big box stores, through construction suppliers, and online.
Online is the best place to start. Manufacturers have websites that provide a full catalog of their products for you to browse at your leisure. Once you find one you like, you can research stores and suppliers in your local area that carry them or that can order them. You can also request samples to take home to ensure they match your expectations and house.
The cost part is simple. Shingles come in bundles that cover 33 square feet. A bundle is a standard unit of shingle material, so all asphalt shingles come in these bundles. The number of shingles in a bundle varies, but it’s usually about 15 to 25 shingles. To figure costs, you apply the 10% to 20% waste factor to the total square footage of your roof. Then divide that number by 33 to get the number of bundles you need. you can also read our article titled cost estimate for roof shingles for more detailed information.
You might come across the term square in your discussions and shopping for shingles. The roof square is a traditional imperial unit that’s equal to 100 square. Roofers still use this terminology and declare shingle coverage and area in squares. The average roof in the U.S. is 1,700 square feet and requires about 19 squares of shingles. There are three bundles of shingles to a square.
DIY Vs. Professional Roof Measuring
You can absolutely measure your own roof. The question is, is it really necessary?
It isn’t.
Every roofing contractor I’ve ever known (myself included) gives free estimates, which means we come to your home, measure your roof for free, and give you a ballpark estimate of what we’d charge to replace it. Since we do this for a living, we’re pretty good at it.
I don’t say that to discourage anyone wanting to estimate their own roof. Rather, I’m pointing out we exist to unburden homeowners of having to do things like this. Roofs are dangerous and incorrect estimation can be costly or prolong projects. So, let a professional roofer handle it.
So, What Is the Best Way To Measure Shingles?
The best way is the simplest: a measuring tape and a pencil. The math is easy, and anyone can do it. It’s something you can do yourself or it’s something you can have a professional do, and whatever you choose will work fine and likely yield the same results.
If you intend to hire a professional to do your roof, I wouldn’t bother measuring for shingles. The contractor will do it, so it’ll be a wasted effort on your part. Letting a professional measure your roof means you don’t have to worry about it — and offers you the peace of mind that your roof will be measured safely and accurately.
FAQs About Measuring a Roof for Shingles
What are the dimensions of a shingle?
Generally, they’re 12 inches x 36 inches, but this can vary by manufacturer and style. However, a firmer rule is that a bundle of shingles covers 33 square feet.
What is the difference between a square roof and a sloped roof?
There is no such thing as a square roof. Although roofs and houses generally seem square, it’s not that simple. Some houses or parts of houses are atypically shaped, like hexagonal or octagonal. However, that has nothing to do with the roof slope. The opposite of a sloped roof is a flat roof.
How do you measure the width of a roof?
The width of a roof is the width of the house plus the roof overhangs on each side. This isn’t a very useful measurement, though, unless you’re mathematically calculating the area of the roof based on the slope and span (which isn’t the preferred method of professionals for calculating total roof area.)
