How to Calculate the Roofing Shingles for a House by Square Feet

A roof is measured in terms of the number of "squares" it takes to cover the surface area. One square equals 100 square feet. Most shingles are sold in "bundles," and it typically takes three bundles to make one square. Some shingles come in bundle groupings other than three, but most do not. Climbing on the roof to measure the surface area is the most difficult part of the process. Have someone help you by holding the tape measure in place.

A good estimate ensures you have enough shingles on hand without over buying.

Step 1

Climb onto the roof using a ladder. Be very careful. Working at any elevation is dangerous.

Step 2

Measure the length and width of the roof surfaces. Record each measurement on a pad of paper. If the opposite side of the roof mirrors the one you measured, you need only measure one of the two sides. Record the length and width of both sides on your pad.

Step 3

Multiply the length times the width for each roof section to get the square footage for each section. Record the results. Use a calculator to make the math faster.

Step 4

Add up all the square footage calculations for all roof sections. The result is the total square footage of the roof.

Step 5

Add an additional 10 to 15 percent to account for waste and the extra shingles you will need for roof caps and starter rows. Lean toward the higher percentage for roofs that have hips and valleys.

Step 6

Divide the total square footage calculation by 100 to get the number of squares necessary to cover the roof.

Step 7

Multiply the number of squares by 3 to get the number of bundles you will need to purchase from your home center or roofing supplier.


  • Use caution any time you enter, walk on or leave a roof. The slope makes it easy to lose your footing and fall. Some roofs, such as shake shingled ones, can be slippery if wet or aged.
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