How To Measure A Roof For Shingles (Step-By-Step Guide)
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How to Measure a Roof For Shingles (Step-By-Step Guide)

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Posted By: Roof Troopers

contractor on roof cuts shingles after measuring

If you think of yourself as handy around the house, then learning how to measure a roof for shingles is an essential skill to have in your pocket. After all, you don’t want to have to worry about things like overspending or running out of shingles halfway through a roof repair — and you certainly don’t want to just “eyeball it” as it’s a job that requires precision.

Consider this your step-by-step guide for measuring your roof for replacement shingles. Read on to learn more.

Measuring Your Roof for Shingles: Getting Started

The first thing you need to know about measuring for roof shingles is that roof surfaces are measured in “squares,” with each square being equal to 100 square feet. Having said that, it’s all too easy to hop online and find a handy roof square footage calculator or shingle calculator. 

However, if you don’t know how to measure a roof, these online calculators won’t do you any good. Even if you have an idea of your total square footage, the measurements you enter into the calculator will likely be incorrect. This can cause you to purchase either too many shingles or not enough (but it’s always better to have extra.)

Therefore, the best method for measuring your roof involves safely climbing up your roof with a measuring tape, notepad, and pencil. Ultimately, you’ll need to measure each plane of your roof before you can calculate the square footage to determine the number of shingle bundles you’ll need to purchase.

The Tools and Materials You’ll Need

Before getting started, you’ll also need the following tools and materials:

contractor measures roof square footage for shingles
  • A measuring tape
  • Notepad
  • Pencil
  • Ladder
  • Fall-arrest equipment

Once you have everything you need, you can proceed with the following steps.

Get Set Up Safely

Safety should be your first priority as you’ll be working from a substantial height. So, be sure to set your ladder up on level ground, with the base extending out at least three feet from your roof’s edge. 

As for your fall arrest equipment, it’s good to include:

  • A harness
  • Shock absorption lanyard
  • Braided rope
  • A buddy to hold the ladder steady and be there to call emergency services in the event of an accident

Remember — you always want to maintain at least three points of contact as you climb up and move around. So, secure your measuring tools in a pocket while getting up there.

Measure Square Footage 

Once you get up to your roof, walk all the way up to its peak. This will allow you to orient an overhead sketch on your notepad and ensure that you label each plane correctly. 

Choose a section of your roof to start with and lay your measuring tape along the length of the plane. Take note of the measurement and its corresponding location, and then do the same for the width of the plane. Repeat this process for each plane.

Calculate the Square Footage

Once you have your measurements, you can go ahead and calculate the square footage of each plane. However, not all roof planes are the same. Some are square, while others may be in the shape of a rectangle, trapezoid, or even triangle.

Therefore, you’ll need to use the formula that applies to your roof:

Formula for the area of a rectangle or square:

A = L x W
Area = Length x Width

Formula for the area of a trapezoid:

A = [(B1 + B2) x H] / 2
Area = [(Top + Bottom) x Height] / 2

Formula for area of a triangle:

A = (B x H) / 2
Area = (Base x Height) / 2

Once you’ve calculated the area of each roof place, you can use the information to calculate your roof’s total square footage. To do this, you can simply add the area of each plane together, and you’ll have the sum of the total square footage of your roof.

Calculate the Roofing Squares

contractor measures roof shingles before installing

Once you have your roof’s square footage, you’ll need to convert it into roofing squares. This is because shingle bundles are listed for purchase as a covering of up to ⅓ of a square. Therefore, a square of shingles in roofing terms equates to approximately 100 square feet.

This is when you can fall back on a (square) calculator to make the conversion. Or, you can simply divide the total square footage by 100.

For example, a roof measuring 1,987 square feet would be converted into 19.87 squares.

Determine the Number of Shingle Bundles You’ll Need

The next step is to figure out how many shingle bundles you’ll need to make your repairs. Remember, a bundle of shingles covers about ⅓ of a roofing square. This makes it pretty easy to do the math.

All you have to do is multiply the number of roofing squares by three. So, if your roof’s area works out to 20 roofing squares, you’ll need 60 bundles of shingles.

Calculate the Amount of Roofing Felt You’ll Need

When making repairs or replacing whole areas of your roofing, shingles aren’t the only thing you’ll need. There’s also the underlay (or felt) that gets installed beneath the shingles to take care of.

Roofing felt typically comes in 15- or 30-pound rolls. 15-pound rolls cover up to four squares, while 30-pound rolls cover up to two squares. So, if you’re using 15-pound roofing felt, you’ll need to divide your total number of roofing squares by four. If you’re using the 30-pound roll, you would divide the total by two. This will tell you how many rolls you’ll need.

Account for Waste

Once again, you’ll likely need to account for roof angles that require you to modify your shingles so no gaps are left behind. Since you’ll have to cut shingles to fit them into certain angles, it’s also highly likely you’ll make a few mistakes.

Therefore, it’s always recommended that you tack on at least 15 percent more material than your calculations call for. So, whatever your total is, multiply it by 1.15 and then add that number to the original total. (Be sure to round up to the nearest whole number!)

No One Said Measuring For Roof Shingles Was Easy

If measuring for roof shingles sounds difficult, it’s because it is. Not only is it risky to climb up on your roof, but it involves quite a bit of math. Plus, replacing roof shingles often becomes costly and frustrating for first-timers.

Have the roofing experts at Roof Troopers take care of your shingle replacement instead. We have the experience and equipment to take accurate measurements and gather the right amount of materials. Reach out to us today to get a free quote!


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