How Big is a Square in Roofing? Measuring for Shingles (Square Feet)

Planning to find out how much a new roof would cost you and you need to measure your roof’s area or find out how big is a square of shingles? Well then, you have come to the right place.

Installing a new roof on your own is never a good idea. Yes, replacing a few shingles here and there on your existing roof is quite easy but since this is such a huge investment, it is better to call a professional roofer.

If you are a DIYer though and want to start such a project, then read on as we provide some very useful tips.

In order for your roofing project to be successful, you need to invest in both ­— your money and time. It is completely understandable that you would want to find out how much a roof costs.

We would like to warn you beforehand that roofing estimations can be quite difficult to decipher, which is why we are going to be straightforward.

How Roof Area is Measured?

In order to find out how many shingles your roof will require, you first need to estimate its total square footage. This is done in three easy steps:

1. Start by measuring the width and length of your roof (including dormers).
2. Multiply width x length (this will give you the roof’s square footage of one plane).
3. To calculate the total square footage of the roof, add up every plane’s square footage.

Here are a few examples of different roof types:

Example #1

The above figure shows a shed roof. This type of roof has a single plane. In order to determine this roof’s square footage, here’s what you need to do:

• (A) length x (B) width: A x B
• 140′ x 100′ = 14,000 sq. ft.

This is the roof’s total square footage.

Example #2

The above figure shows a gable roof. A gable roof has two surface planes as indicated by A and B. In order to determine this roof’s square footage, here’s what you need to do:

• Plane1: 140′ x 100′ = 14,000 sq. ft.
• Plane2: 140′ x 100′ = 14,000 sq. ft.
• Plane 1 + 2 = 28,000 sq. ft.

This is the roof’s total square footage for two planes.

How Big is a Square in Roofing?

The calculations above will give you the total number of square feet of the roof area.

As you have noticed in the roofing industry however, the surface of the roof is being measured in “squares”. This refers to the roof area that measures approximately 100 square feet.

Therefore: 1 Square in Roofing  = 100 square feet

Now, in order to determine how many squares are there on the gable roof for example, all you need to do is divide the total square footage by 100.

• Total square footage from Example 2 above: 28,000 sq. ft.
• Number of squares for 2 planes: 28,000 sq. ft. ÷ 100 = 280 squares

This means that both planes of the roof will require 280 squares of shingles. A three-tab shingle, which is most commonly used, is packed in 3 bundles per square.

How Many Shingles are in a Square?

When the time comes to buy shingles for your roof, keep in mind that they are usually sold by the “bundle”. Each bundle is a wrapped package of shingles with such a weight as to be lifted easily by a person.

The most common is to have three bundles of shingles for a square of roof area. In other words, if you buy 3 bundles of shingles, this will cover one square which is 100 sq.ft of area.

The most usual case when buying standard shingles (i.e three-tab strip shingles and laminated shingles), there are 29 standard-sized shingles (12 in. by 36 in.) in each bundle.

Summary of the above: 

1 Square of Roof = Covers 100 sq.ft area = Need 3 bundles of standard shingles (usually) 

How Much Roofing Underlayment

Up till now, we were discussing how to measure roofing shingles for re-roofing. When talking about a new roof, the same amount of square footage is required for the underlayment.

You will find underlayment in rolls of four squares each. In order to determine how many rolls of underlayment you would need, you need to divide the number of squares for 2 planes by rolls of one square.

• Rolls of underlayment required: 280 sq. ÷ 4 = 70 rolls

If you are applying the shingles over an asphalt roof, then you don’t need underlayment.

Pro Tip: In order to avoid any delays in installment due to shortage of shingles, add 10% to the total material requirement for trim allowance.

Determining the Slope

Now that we are done with the planes, let’s move on to the slope. As you can see in the figure above, the slope is the plane’s decline. This is measured from the deck’s vertical rise — 12″ over the horizontal distance.

Let’s say the rise of your roof is 5″, then the slope of the roof is 5 in 12. If the roof is steep, then a different method is used to measure the roof.

Here, you will measure the roof’s exterior walls + the overhanging that is parallel to house’s ridge. To mark the eave, throw a thick rope over the house’s ridge and then calculate the width dimension. Calculate all the horizontal edges this way and you will get the total area.

How Many Nails Required?

After you are done calculating the total square footage, you need to determine the number of nails you will need.

Usually 4 nails are used per shingle. As mentioned earlier, shingles come in three tabs, which means you would need around 1,120 nails/sq.

If you live in a high windy area, then you will need 6 nails per shingle, which brings the count to 1,680 nails/sq.

This calculation is based on 280 shingle squares, according to the gable roof measurement. For the right nailing pattern, refer to the instructions that comes with the shingles.

And this is how you measure your roof area and the number of shingles and nails needed. If you are looking for more informatory articles such as this, then visit Epic Home Ideas.