How to Estimate Your Roof's Square Footage

Determining the square footage of your roof is an important step in getting accurate estimates for repairs or a full roof replacement. While a professional roofer will take precise measurements before any work begins, you may want to calculate a rough estimate on your own. This way, you can feel confident in the roofing estimates you receive and make informed decisions about your roofing needs. 

When dealing with your roof, safety is key—always use caution when measuring, and call in the professionals if you need help.

Tools for Measuring a Roof

There are a few basic tools required to get started measuring a roof: 

• Long tape measure (ideally 25 feet or longer)
• Ladder (make sure it’s sturdy and tall enough for safe access to the roof)
• Calculator (to do the math)
• Pencil and paper (for sketching and taking notes)
• Safety gear (such as gloves and non-slip shoes)

Not all roofs are easy to access, and it is important to always prioritize safety. If you feel uncomfortable climbing onto your roof, try measuring from the ground or call a professional.

Calculate the Square Footage of a Roof

While measuring a roof can seem complicated, breaking it down into steps makes the process manageable. The how-to steps below take into account factors like roof slope, shape, and special features such as chimneys to help you get a rough estimate.

1. Measure the Ground Area  

Begin by measuring the length and width of the house from the ground. This is the simplest part of the process and can be done using a tape measure. If you have a basic rectangular house, you’re in luck—this makes the math easier. For example, if your house is 40 feet long and 30 feet wide, you would start with an area of 1,200 square feet (40 x 30).

If the house is not a simple rectangle, you can break the home’s footprint down into sections that are easier to measure, like rectangles, squares, or triangles and calculate the area for each section separately.

2. Factor in the Roof Slope  

Most roofs are not perfectly flat. If the roof has a slope, you will need to adjust the ground area measurement to account for the extra surface area. The steeper the roof, the larger the surface area. To do this, you’ll need to calculate the roof pitch. Here’s a simple way to do it:

• Measure the rise (vertical distance) over a 12-inch horizontal span (called the run). For example, if your roof rises 6 inches for every 12 inches of run, your pitch is 6/12. 
• Once you have the pitch, you can find the slope factor using an online calculator or reference table. For a 6/12 pitch, the slope factor is about 1.12.
• Multiply the ground area by the slope factor to adjust for the roof’s incline. In our example, you would multiply 1,200 square feet by 1.12, which equals 1,344 square feet of roof area.

3. Consider Roof Shape and Features  

In addition to having different slopes, roofs come in various shapes, which can complicate the measuring process. If your roof is a simple gable roof (two slopes meeting at a ridge), estimating the square footage is relatively straightforward. But if you have a more complex roof with features like dormers, valleys, or multiple gables, you will need to break the roof down into sections and measure each one separately. Sketching out your roof and labeling the estimated square footage for each section will help you stay organized.

• Gable roof: Simply measure the length and width of each slope and add them together.
• Hip roof: Measure each triangular section separately and use the formula for the area of a triangle (½ base x height).
• Complex roofs: For roofs with many different sections, measure each part individually and add all the areas together for a total.

4. Account for Overhangs  

Roofs often extend beyond the edges of the house, and these overhangs add to the square footage. Measure the overhang from the outside wall to the edge of the roof and add this to the total measurements. If the overhang is 1 foot around the entire roof, for example, you would add 2 feet to both the length and width measurements before calculating the area.

5. Adjust for Roof Features  

If your roof has skylights, chimneys, or other features, you will need to subtract the square footage they take up. Measure the area of these features and subtract it from the total roof area. For example, if a chimney takes up 10 square feet on the roof, subtract that from the final measurement.

Tips for More Accurate Roofing Estimates

Advances in technology have made DIY roof measurements even easier. For instance, if you have access to a drone, you can use it to take aerial photos of the roof. These images can help you see the shape and layout of the roof without climbing onto it. 

There are online tools and apps that use satellite imagery to estimate your roof’s size. These aren’t always 100% accurate but can provide a rough estimate if you prefer not to measure manually. Sometimes there is a charge for using these services, so be sure to read the fine print. 

Why a Professional Should Measure Your Roof

While DIY roofing measurements can give you a ballpark figure, it is important to have a licensed professional roofer take precise measurements before any work is done. Pros have the experience and tools to measure accurately, which can save you money in the long run. 

The roofing contractor will also help you understand the factors that affect roofing costs beyond just square footage. These include local building codes, choice of roofing material, ventilation and drainage options, and more. 

Be wary of any contractor who gives you an estimate without physically measuring your roof. Guessing or using outdated measurements can lead to inaccurate estimates and unexpected costs. A reputable roofing company will take the time to measure the roof accurately and provide a free inspection in addition to measurements. This way, you will have all the information you need to determine the next steps for your roof repair or replacement. 

Contact Honest Abe Roofing to Get Started

Estimating your roof’s square footage yourself is a great way to prepare for a roofing project, but it’s only the first step. With your estimate in mind, reach out to the trusted professionals at Honest Abe Roofing for a final measurement and quote you can rely on.