How to Estimate Roof Square Footage

Have you ever wondered how to estimate the square footage of your roof surface? Many people never worry about these things or believe they can look them up online when necessary. However, that’s usually not the case.

There are many reasons to know the roof’s square footage. You might be trying to figure out how many roofing shingles you need for your project. Likewise, you may want to hang holiday lights or hope to install a roof drip edge. Regardless, the process isn’t as straightforward as you might think.

Though it will take some math, you will find your roof measurements (square footage) with this helpful guide. However, working with a roofing professional might be wise if you plan to put on a new roof. They will do things correctly, saving you time, money, and effort while reducing stress.

Why Would You Need to Know Your Roof’s Square Footage?

Most homeowners rarely consider the roof’s square footage until they require a replacement or major repairs. When you know the size of the roof, you can:

• Determine the roofing materials you should buy
• Get accurate quotes from contractors
• Weigh the cost of varying roofing materials
• Set a budget for your project

Overall, the roof replacement cost depends mainly on the roof’s square footage. If you measure it and determine it’s more than expected, you may consider an alternative roofing material to lower your price. It’s crucial to have an idea of the options before diving in.

What’s a Roofing Square?

Before learning to measure the square footage, you should understand a roofing square. While you might assume that a roofing square equals a square foot, that’s not true! Understanding the differences between those measurements is crucial.

In terms of roofing, one square refers to a full 100-square-foot area. Therefore, a 2,000-square-foot roof requires 20 squares of the roofing material you prefer.

Measuring the Roof’s Square Footage

Though you can always grab a measuring tape and climb onto the roof to get the exact square footage, it’s often easier and safer to make calculations from the ground. Usually, approximate numbers are good enough when you’re creating a generalized budget for your project.

However, you will need a more accurate measurement if you’re ordering shingles or building roof trusses. Follow the steps below to learn how to measure a roof:

Find the Home’s Square Footage

Look at the home’s square footage to get an approximate roof square footage number. It won’t be entirely accurate if you have an irregularly shaped, sloped, or overhanging roof, but it will give you a good idea.

Here are the steps to get your square footage:

1. Measure the home’s length.
2. Measure the home’s width.
3. Multiply those numbers together.

Those steps work well if you have a rectangular roof. However, you must break things up into geometric areas if it’s any other shape. Calculate the square footage in each area, adding those together.

Measure Your Roof Pitch

When you know the home’s square footage, you must also determine the roof pitch to get an accurate measurement. The pitch is similar to the roof slope but not the same. Instead, the pitch is where the roof rises vertically (vertical rise) of the roof. This number is divided by your horizontal run.

Overall, you must examine how many inches the roof rises per foot. If you have a roof pitch 5/12, the roof will rise 5 inches for every 12 inches.

You might find your roof pitch on building plans and blueprints. Otherwise, you must calculate it, requiring you to be on the roof. This is very dangerous, and you shouldn’t do so unless you have the skills and tools for the job. However, if you’ve got a ladder and want to try, follow these steps:

1. Mark 12 inches with a measuring tape on your significant level.
2. Set up the ladder carefully.
3. Ask someone to hold your ladder while you climb to the roof.
4. Once on the roof, hold the level horizontally, firmly placing one edge against the roof’s slope.
5. Adjust the level to be level, ensuring the edge continues touching the roof.
6. Find that 12-inch mark you made earlier.
7. Measure the distance (vertically) between the roof and the 12-inch mark on the level.
8. Divide the number you get by 12.

For example, there are 7 inches between the roof and the 12-inch mark you made on the level. Therefore, you have a roof pitch of 7/12.

Consider the Slope Factor

Unless the roof is flat, you must account for the slope to get the square footage. Therefore, you’ll use the roof pitch number to find the pitch multiplier number.

The pitch multiplier will vary based on the complexity and steepness of the roof. A less severe slope will have a lower number.

It’s wise to use an online pitch multiplier table to find your figure, but here are some common ones:

• Roof pitch of 1/12 – Pitch multiplier of 1.00
• Roof pitch of 7/12 – Pitch multiplier of 1.15
• Roof pitch of 14/12 – Pitch multiplier of 1.537

Gable Roof

A gable roof is one of the most popular options. It features two sloped panels and two flat sides. For a walkable gable roof like this, the slope correction number, such as 1.3 or less, will generally be low.

Steep Roof (Complex Shapes)

Sometimes, roofs have complex shapes or are very steep. If yours is steeper than average, the figure will be more than 1.6 in most cases.

Hip Roof

A hip roof has all sides that are sloped. Therefore, you may have to calculate each pitch separately. The pitch multiplier will likely be 1.4 or less.

Calculate the Square Footage of Your Roof

Doing the math once you’ve got the roof pitch multiplier would be best. To find the total square footage of the roof, you must multiply the home’s total square footage and the pitch multiplier. The formula looks like this:

Pitch multiplier x Home square footage = Your roof square footage

For example, you have a 1,000-square-foot home with a roof pitch of 2/12. Therefore, the pitch multiplier is 1.014 (you looked that up online). The roof would measure roughly 1,014 square feet.

It’s wise to get an accurate number by splitting the roof into geometric sections. You’ll use that formula on each one.

Important Factors That Might Impact the Cost of a Roof Replacement

Square footage can impact the cost you pay for a new roof. However, here are a few other factors that might change the price:

Type of Roof

The roof type you choose can impact the price you pay. Many roof options are available, and you must consider your budget and style.

Those who want affordability will likely choose asphalt shingles. However, upgrading to something that lasts longer might be wise, so that a metal roof might be the right choice.

Metal and asphalt shingles are the most common roof types, but there are other premium materials. Tile, slate, and cedar shake can offer a more unique look, which costs more.

Time and Labor to Finish the Job

Time and labor are the main factors when determining the price of a new roof. Though you might be focused on the material cost, you will also have to pay the contractor for their work. Prices are based on experience, skill level, and how many days it takes to do the project. This varies between professionals.

Tips for Measuring the Roof Square Footage

Most homeowners don’t have simple roofs. Therefore, they can use these tips to help them get accurate measurements:

Section the Roof

When calculating roof area, you might want to get the square footage of different sections and add those measurements. This is especially helpful if the different roof area options have varying roof pitches. For example, you’ll probably have to section the roof if it has multiple sections, hip ridges, or dormers.

Remember the Dormers

Dormers are separate roof sections for the upper-level windows. Make sure you’ve factored them and other features into the calculation for square footage. You won’t have to consider pipes and chimneys because the contractor usually works around them.

Consider Overhang

Many roofs have slight overhangs over the exterior walls. Therefore, the square footage on the floor plan (or what you measure yourself) might be a little smaller than the actual square footage. To get accurate measurements, you’ll need to measure your roof overhang and add it to the width and length measurements before calculating your square footage.

DIY or Hire a Roofing Contractor

Homeowners can often estimate the approximate square footage of the roof. This is simple if they have the blueprints or floor plans. However, you may need accuracy, especially if you’re installing a metal roof or installing a new one.

Typically, working with someone who understands the roofing industry is wise. A roofing contractor can help you get the square footage because they will measure each section by hand. Likewise, they have the tools and skills to do this safely.

Please call WDR at (512) 820-6505 to request a free inspection and project quote today!

FAQs About Estimating the Roof’s Square Footage