Menu Close

How To Measure a Roof for Shingles?

Knowing how to measure a roof for shingles will come in handy, if you’re building your own shed, or perhaps want to do a repair on a swath of damaged shingles on your home’s roof, you will need to know how to figure out how many shingles you will need. If you haven’t dealt with this, it may seem a bit confusing, especially if you have a roof with a few complications, such as valleys or gables.

The first thing you need to do is figure out your area that will need shingles. This means getting on the roof with a measuring tape and notebook. If you will need to work on more than one area, you might draw out a diagram so that you have the right measurements for each area of the roof. Measure the width and length of each section, writing them down as you go along. You might add the measurements to your diagram as well.

A rectangular space will be figured as the width times the height to get the square footage. If your measurements include both feet and inches, convert the whole measurement to inches, then convert it back to feet once you have the multiplication.

Ryans Shed Plans

Odd-shaped spaces need a little more work. A trapezoid will be measured by adding the top and bottom measurements, multiplying by the height, then dividing that answer by two. A triangle is the base times the height divided by two.

How to Measure a Gable Roof for Shingles

Your gable roof will have two planes or sides. Measure the width times the length for each and add the two numbers together. Your roof ridge will be the same length as your roof planes. Your two planes should be equal to each other; however, if you have any doubt, it wouldn’t hurt to measure both to make sure there are no surprises later if you have any doubt.

How to Measure a Roof for Shingles with Valleys

When measuring your roof, make a note of the length of the valleys. This is especially important if you plan to use special materials such as valley metal in the valleys. The extra shingles you figure into your estimate will cover the special trimming you’ll need for the shingles in the valleys if not.

3 Main Methods of Shingling Valleys

Method Number1] Use a wide metal flashing and cut the shingles on both sides of the valley to leave a 3-to-4-inch section of the metal exposed. Depending on the number and length of the valleys add half a bundle of shingles per 10 feet of valleys.

Method Number 2] This method is to weave the shingles across the valley letting the shingles go up the other side of the valley on both sides. Figure on an extra bundle of shingles per 10 feet of valley.

Method Number 3] Run one side of valley shingles thru the valley and up the other side. Then you run the other side thru and snap a line and cut them off. This method will require about an extra bundle of shingles per 20 feet of valley. When using this method shingle the smaller valleys first running the shingles up the bigger side and cutting the valley shingle on the large side.

How to Measure a Hip Roof for Shingles

Your hip roof will have four planes, two trapezoidal main sides, and two triangles on the ends. A trapezoid will be measured by adding the top and bottom measurements, multiplying by the height, then dividing that answer by two. A triangle is the base times the height divided by two. Add the totals together to get the total square footage. Be sure to measure the ridge individually.

How Many Squares of Shingles Do I Need?

A roofing square equals 100 square feet. You’ll likely not end up with so many squares plus an odd amount. You should get at least fifteen percent more shingles than your measurements call for to cover any contingencies, such as damaged shingles in a bundle or the extras you’ll need to cut along the roof edges and to fit into valleys.

How Many Bundles of Shingles Do I Need?

Once you have your measurements, you can calculate the shingles. You may have heard shingles measured by the square. A roofing square is 100 square feet. Each shingle bundle will usually cover a third of a square, so you multiply the number of roofing squares by three. Allow an additional fifteen percent for waste. Also, some shingles may be cracked or damaged when you get them, and the extra will cover that possibility. In case you’re wondering, there are usually 29 shingles in each bundle.

Buy a Shed or Build

Allowing extra shingles is especially important with an odd-shaped area or valleys, as you’ll need to cut some shingles to fit in the area. Whether you use the woven method or cut method in the valleys, the number of shingles needed will be about the same.

How Many Shingles for Waste and Ridge Capping?

As has been noted, you should add another fifteen percent to the total of your shingle estimate to cover any waste when having to cut shingles to fit, and also cover any damaged shingles that may come cracked or may crack when your helper drops them.

Ridge capping shingles are specifically formed to fit the ridge of the roof. While some people advocate using regular shingles on the ridge cap, many types will crack when you try to bend them over the ridge. Ridge capping shingles are not only formed to fit the ridge bend but they are also thicker than the other shingles to add protection for the roof and the rest of the shingles. It’s much better to get ridge cap shingles for peace of mind and good protection.

To figure out how many ridge capping shingles you’ll need, measure the hips and ridges. Ridge capping shingles are usually one-foot square and are installed with an overlap so that the exposed part is five inches long for each. Figuring the number of ridge cap shingles can be done in more than one way. One way is to multiply the total ridge length by twelve, then divide it by five. If you have any doubts, bring your measurements with you to your supplier and he’ll help you figure it out.

Do I Need Underlayment Under the Shingles?

Underlayment is an important part of a roofing project. Some people will try to skip the underlayment to save money, but this can be very costly in the long run. Unless you want to get on the roof every time a few hailstones fall or a branch hits your roof, you probably will have a cracked shingle or two on your roof from time to time.

If you don’t have underlayment, moisture will seep into the crack, seep into your roof decking and eventually cause mold, mildew and rot. It also is a way for insects to get in.

If moisture gets in because of an undiscovered cracked or broken shingle, you’ll eventually have a more expensive roofing project to replace the damaged decking that will end up costing more in materials and labor than the underlayment would have cost. Since a roof is something that you want to last a long time, why skimp on it?

Ryans Shed Plans

Your roof measurements not only apply to the shingles but also to figure the number of rolls of underlayment you’ll need. Typically, a 15-pound roll of underlayment will cover about four squares. Again, you’ll want to allow about fifteen percent more to cover accidental tears or cover odd shapes.

What Type of Nails Do I Use for Installing Shingles?

Ring roofing nails that are made from hot-dipped galvanized steel are the accepted norm for roofing nails. They should be at least 12-gauge in thickness. The length will depend on the thickness of the shingles and the roof sheathing. You’ll want to make sure that the nails penetrate deeply enough to ensure that they will stay put.

When figuring out your nails, this can depend on the type of shingles you plan to use. Most roofers use five nails per starter shingle on the edges, and four nails on the rest of the shingles. This averages out to 320 nails per square for common three-tab shingles. Of course, you’ll need a little extra for any flashing around air vents or chimneys.

Is It Better to Use a Nail Gun or Hand Nail?

Any time you see a roofing crew at work, they’ll likely be using nail guns. The workers move quickly over the roof, nailing as they go. This may seem like a great way to save time and get the job done, but is it the best way?

Nail guns seem easy to work with, but they actually take some practice to use effectively. They do have a kick, and it takes a bit of practice to get the nails exactly where you want them. You also have to learn how to operate the gun so that all the nails are driven straight. That fast-moving crew with nail guns may not be working very carefully. In fact, it’s estimated that over 60 percent of all roof repairs are due to shingles not being properly air-nailed in.

Most are powered by air compressors. The nails are driven by a set amount of air pressure. The compressor comes on periodically when the nail gun pressure gets too low. Nail guns also have varying pressure, which is adjusted for the type of wood, type of shingles, and even the weather conditions. Getting the right pressure can be tricky. It may also need to be adjusted periodically as the job goes on. You could probably rent both a compressor and a nail gun from a tool rental store.

Ryans Shed Plans

One problem with nail guns that people aren’t aware of is that there is a limited area on each shingle meant for nail placement. If you miss and nail some shingles in the wrong place, it can cause problems with leakage and moisture seeping in under the shingles. Some shingle manufacturers will actually void their warranty if shingles on a roof were nailed improperly.

Another problem is missing the rafter. Shingle nails are usually driven through the decking into the rafter below. If you’re hand nailing and miss a rafter, you can tell and correct the problem. If you’re using a nail gun, you likely won’t know if you miss the rafter.

Basically, if you’ve got experience with a nail gun and feel comfortable using one, by all means, go ahead. If you haven’t used one before, it may be wise to be in less of a hurry to finish the job and do a more careful job with hand nailing. You’ll be sure that the job was done right.


Measuring roofing is a lot like other aspects of construction. If you’re a newbie, some of it may seem confusing, but once you get into it, it’ll make more sense. Besides, there’s nothing wrong with learning a new skill.

Related Reading

Rolled Roofing Vs 3-Tab Shingles