How Is a Roof Measured? Squares, Pitch, Waste and Aerial Reports

How is a roof measured, step by step?

Measure each roof section, correct for pitch, add the sections, divide by 100, then add waste.

Here is the method that Owens Corning, JobNimbus and aerial report makers all describe, in order.

1. Measure each roof section

   Measure the length and width of each flat section of the roof, including dormers and additions. Owens Corning's gable example is two planes of 40 by 30 feet each, which is 2,400 square feet. Measuring one plane at a time is more accurate than measuring the whole house.

2. Find the pitch of each section

   Pitch changes the real surface area. A porch at 3:12 and a main roof at 8:12 need different factors. Our page on roof pitch shows how to find it.

3. Apply the pitch factor

   If you measured the footprint, multiply by the pitch factor. Owens Corning lists 1.118 for a 6:12 roof and 1.414 for 12:12. If you measured each sloped plane directly, skip this step. JobNimbus warns to check whether an aerial report already includes pitch, so you do not count it twice.

4. Add the sections and divide by 100

   Add all the areas, then divide by 100. That is the number of squares.

5. Add waste

   JobNimbus suggests 10 percent for a simple gable, 10 to 15 percent for a hip roof, and 15 to 20 percent for a complex roof with many valleys. Owens Corning says 10 to 15 percent. More cuts means more waste.

6. Measure the edges and ridges too

   The squares number covers the roof surface. Ridge caps, hips, valleys, eaves, rakes and drip edge are measured in linear feet. Aerial reports list these lengths separately.

7. Check it in person

   Pictures can miss things. Trees, chimneys and add-ons hide parts of the roof. A good roofer checks the report against the actual roof before ordering.

For ordering, Owens Corning notes that laminate shingles ship at three bundles per square, so 24 squares is 72 bundles before waste.

How accurate are satellite roof measurements?

Vendor tests report about 98 percent accuracy on clear homes. The same companies tell users to check the measurements when trees or poor images get in the way.

In 2025 EagleView announced a comparison against independent LiDAR measurements by a surveying firm. In a set of Denver area single-family homes, it reported 98.43 percent accuracy on roof area (an average difference of 5.61 square feet), 98.77 percent on linear measurements, and 98.49 percent on roof slope. The article does not say how many homes were in the sample, and the figures come from EagleView's own announcement.

The company's own sample report is more careful. It says that because of tree coverage, poor images, low resolution or other blockages, the report does not offer an accuracy guarantee, and it recommends that anyone using it check the yellow-shaded sections in person. A roof under big trees is exactly the case where imagery gets blocked.

The same sample report ends with a comment saying that, because of obstructions in the available images, the user should verify measurements on the portion of the structure highlighted in yellow. Hover's page, for its part, lists no limits at all, which is why a vendor's claims alone are not enough.

So the sound approach is to use a report to start, then confirm on the roof or by drone before ordering. That is also why the number on your quote can change a little at tear-off.