How to Calculate Roofing Square Footage

If you find yourself in need of a new roof and want to figure out how much it’ll cost you, (without calling out a roofing professional…yet) there are a few calculations you can make to figure out how much roofing material you may need, including roofing shingles (ie shingles per square foot), ridge caps and more.

To do this, you’ll need to calculate the total area of ​​your roof. But first, you need to identify your roof pitch. Here’s how to do it correctly:

Step 1. Measure the Roof Pitch

To accurately calculate the area of ​​your roof, first you need to start taking measurements of your roof’s pitch (or your roof slope). To do this you’ll need the following materials:

  • ladder
  • measuring tape
  • large level

Then, follow these steps:

Step 1. First, you’ll need a measuring tape and a large level. Use your measuring tape to measure 12 inches on the level and make a mark at the 12-inch line.

Step 2. Next, you’ll need a ladder. Set the ladder against the gable end of the roof. Make sure to take the appropriate safety precautions when doing this, especially if you have a steep roof.

Step 3. Climb to the top of your roof and place your level against the gable roof and flat against the side of your home.

Pro Tip: Wondering what exactly a gable roof or gable trim is? This is used to finish off the edge of the upper portion of a sidewall that comes to a triangular point at the ridge of a sloping roof plane.

Step 5. Now it’s time to calculate the rise of your roof. To do this, use the measuring tape to measure from the 12-inch mark on your level up to the bottom edge of your gable trim.

Step 2. Estimate Your Roof Area

Once you have your roof pitch this will help eliminate a lot of extra measurements because you can use the roof pitch to get an estimated square footage of your roof:

Step 1. Use the number you landed on for your roof’s pitch, then divide the number by 12.

For example, if your roof’s pitch is 6 in 12, you would divide 6 by 12. The resulting number would be 1/2.

Step 2. Then, square your result.

For example, if your number is 1/2, then squared would be 1/4

Step 3. Add 1 to your number. (1/4 + 1 = 10/4.)

Step 4. Now it’s time to figure out the square root of your new number.

Using our example, the square root of 10/4 is 1.58

Step 5. Next you’ll want to figure out the square footage for one of your home. To do this, divide the total square footage of your home by 2.

If you have a 3,000 square foot home, for example, this number would be 1,500.

Step 6. Multiply the square footage of one floor by your square root and voila! You now have the estimated square footage of your roof. (1,500 x 1.58 = 2,370 square feet.)

Step 3. Calculate The Exact Roof Area

To calculate accurate roof measurements that reflect the exactly area and your roof’s total square footage, there’s a way to do this too — it just requires a bit more leg work and you’ll need to know the length and width of your house.

You’ll need your measuring tape and ladder again to do this.

Step 1: Divide your roof pitch by 12, just like we did above.

Step 2: Square your result.

Step 3: After that, add 1 to your number.

Step 4: Calculate the square root of the number above.

Step 5. Use your tape measure to get the length and width (horizontal run) of your house, including any overhangs.

Step 6. Multiply your house length by your house width. The resulting number is your area.

Step 7. Next, multiply the area by your roof’s pitch.

Pro Tip: You’ll want to consider the “waster factor.” Roofing contractors usually add somewhere between 10-15% to the total roof square footage to account for the waste factor, but keep in mind, this calculation can vary based on roof style or other roofing materials.

The most common roof types include:

  • Gable Roof
  • Dutch Gable Roof
  • Gambrel Roof
  • Hip Roof
  • Mansard Roof
  • Shed Roof
  • Flat Roof

Make sure to determine which yours is so you can accurately calculate the waste factor.

About Christian Roofing

Christian Roofing, Inc., is here to provide you with a host of excellent roofing services whether you’re hoping to outfit a seaside cottage or a large corporate warehouse. Our experienced team of roofing professionals is capable of working on any residential, commercial, or industrial project regardless of size or scope.

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