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How to Calculate Roof Square Footage

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Remember being in math class and thinking ‘When will I ever use this in the real world?’  We do too. Geometry class was a snoozefest, but there are some handy things we wished we had paid more attention to. One of  them being the formula for calculating area. This formula is crucial in helping you calculate roof square footage. Remember: length x width.

Why Is Calculating Roof Square Footage Important?

Many roofing companies offer free no-commitment estimates. Sounds good right? Sure thing, what’s better than free? But think for a second, you may know absolutely nothing about roofing. How can you be sure this free estimate is accurate and properly priced? It may not seem important but calculating the square footage of your roof can prove beneficial. Here are a couple of reasons why you should know your roof’s square footage: 

  • Helps you better set a budget for any future roofing projects.
  • Help in choosing the best roofing material for your home.
  • Helps you receive a more accurate quote from your contractor. 
  • Helps you decide how much material you need.

Calculating Roof Square Footage 101

While it is not particularly hard to estimate your square footage, there are times when you need an exact measurement. Say, you’re getting a metal roof. You need the exact measurements to buy the correct amount of material. In order to do so, you will need to account for the pitch and slope of your roof.  [H3]Finding the AreaFinding the area of your roof is not particularly difficult. Anyone can do it! Following these easy steps will ensure exact measurements:

  • Measure the length of your home.
  • Measure the width of your home.
  • Multiply both measurements. 
  • The total of both multiplied numbers equals the total square footage.

What is Roof Pitch? 

The pitch is the vertical rise of the roof divided by its horizontal run. In other words, we want to know how many inches your roof is rising per foot. While you may be able to find the pitch on your blueprints, you may not have them on hand, meaning some handiwork is needed. Here’s a step-by-step guide to help you find the pitch of your roof:

  • First, you need a ladder and remember to have fall protection equipment when going onto the roof. Safety is most important!
  • You will also need a tape measure or ruler for the roof. You will also need a level that must measure at least 12 inches.
  • Hold the level in such a way that one end is flat on the roofing surface.
  • Measure the vertical distance from the roof's surface to the level’s 12-inch mark. The given number will be the rise. 
  • In the end, divide your number by 12. Say the rise is 6 inches, your pitch will be 6/12. 

Don’t Forget the Slope

More likely than not, your roof isn’t flat. If it is, well, more power to you! Less math means less work, which means less headaches. For those out there with non-flat roofs, you need to make sure you account for the slope of your roof when calculating the square footage. Luckily for you, we’ve simplified things by including a roof pitch multiplier table to give you a ballpark estimate!

Roof Pitch Pitch Multiplier
1/12 1.00
2/12 1.014
3/12 1.03
4/12 1.054
5/12 1.08
6/12 1.118
7/12 1.15
8/12 1.202
9/12 1.25
10/12 1.302
11/12 1.35
12/12 1.414
13/12 1.47
14/12 1.537
15/12 1.60
16/12 1.667
17/12 1.73
18/12 1.803
19/12 1.87
20/12 1.944
21/12 2.016
22/12 2.088
23/12 2.162
24/12 2.236

How to Calculate Area by Roof Style

Roofs typically represent an owner's taste and style. This means there is no such thing as a uniform roof. There is no ‘standard’ roof. However, there are a variety of roofs that tend to be more common than others, each one with its unique characteristics. Each roof has its own shape, meaning, different pitches, and slopes. 

Flat Roof

Flat roofs tend to be quite simple. One simply measures the length and width of the roof and multiplies both numbers. It is good to remember that the height and width of the roof don’t always align with the external dimensions of your home. Another pro tip is that flat roofs are not 100% flat. There is still a slight bit of slope and pitch to account for! 

Gable Roof

To find the area of a gable roof, you will need to multiply the width by the height. Once you have that number, you will need to divide it by two, and the remaining number is your area!

Hip Roof

A hip roof is made up of two different shapes: triangles and trapezoids. For the triangle-shaped planes of your roof, you will measure the length (base) and divide it by two. Once you divide your base, you will then multiply it by the height, and the result is your area. An easy way to remember this: half of base times height! 

For the trapezoid sections of your roof, we will need a different formula. For this, you will need the base of the trapezoid. A trapezoid has two different lengths, so you will need to find both. Once you do, you will add both of these, multiply them by the height of your trapezoid-shaped roof, and finally, you guessed it, divide it by two! 

Once you have the area for all four sides, you will need to add them all together to find the total area of your roof. Keep in mind, your hip roof is symmetrical, meaning that you will only need to measure two sides of the roof (one triangle-shaped side as well as one of the trapezoid-shaped sides). 

Tools You'll Need 

No job is complete without the use of a couple of tools and good safety equipment. Using faulty and low-quality tools can pose safety hazards and provide you with misleading results. Always ensure your equipment is in good working condition. 

Tape measure:

This needs to be reliable, accurate, and at the minimum measure up to 12 inches. 

Ladder:

You may be tall, but no one is tall enough to get this job done without a ladder. Make sure you have one on hand or phone a friend. If nothing else works, your local hardware store can always provide you with one for a fee. 

Safety gear:

Safety gear includes a good harness and proper footwear. We recommend non-slip work boots. Oh, and don’t forget a hard hat! It’s best to be safe when dealing with roofs. Your number one goal should be zero harm!

Calculator:

Unless you're a math whizz or want to take time to carry one, we recommend having a calculator on hand. You don’t need anything fancy, the one on your phone will do!

Calculating Roof Square Footage: Major Blunders

No one likes being wrong. Measuring your roof's square footage should be no different. You want and need accurate measurements. Accurate measurements are crucial in saving money, and time, and ensuring the best results. Here are some of the most common mistakes you want to avoid:

Not Sectioning Out Your Roof

A good rule of thumb when calculating roof square footage is to section out parts of your roof. This is especially important when dealing with roofs with different pitches and shapes (think of a hip roof). 

Ignoring Dormers

People tend to forget about dormers when figuring out roof square footage. Remember, even though dormers are separate roof sections, they still matter when it comes to finding an accurate measurement. You can always measure these out separately and add them to the total area. 

Not Accounting for Overhang

Most roofs have what's known as overhangs. Overhang is the roofing edge that goes past the siding of your house. To ensure accuracy, measure the overhang and add it to the length and width of your measurements. 

Improper Safety

A common mistake people often make is ignoring safety precautions. Measuring your roof's square footage requires climbing ladders and other elevated surfaces. Failing to prioritize safety can pose a risk of falling and injury. Don’t compromise yourself and your measurements. Safety always comes first! 

Roof Slope and Pitch

A common mistake is failing to take into account the pitch and slope of your roof. Hardly any roof is completely flat. Ignoring the pitch and slope can lead to under and overestimation. Save yourself time and money by ensuring you take every nook and cranny into account. Leave no stone unturned!

Weather Conditions

Weather can play a factor in obtaining roof measurements, especially with more technologically advanced tools. When using drones or laser tools, avoid using them during less-than-stellar weather conditions.

Not Double Checking Measurements 

It’s crucial to check things twice. Being an inch or two off can lead to an improper estimate. If you overestimate, you spend more money. On the other hand, if you underestimate, you will eventually need to buy more material to ensure you have enough material to work with. Save the hassle and check your work twice. 

Benefits of Hiring a Professional Roofer

Most homeowners can easily estimate roof square footage by looking at their floor plans or blueprints. If not on hand, things can become a bit trickier. That’s when an expert comes in. An expert roofing contractor near you can easily, and more importantly, safely obtain precise square footage. A slippery roof or a missed step can lead to serious injury. Don’t hurt yourself when you can have a professional do the job for you. When faced with potential hazards, it’s best to leave it to the pros. 

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