How to Calculate Total Square Footage of Your Roof. To find your roof’s total square footage: Measure the length and width of each plane on the roof (including dormers) then multiply length times width. Add the square footage of each of the planes together.
Roof surfaces are measured in “squares.” A square is an area of roof which measures 100 square feet. To determine the number of squares on the gable roof above, simply divide its total of 24,000 square feet by 100. The result is 240, and this means you would need 240 squares of shingles to cover that roof.
A square of shingles is the quantity needed to cover 100 sq. ft. of roof. Shingles are packaged in paper- or plastic-wrapped bundles designed to be light enough for a person to carry, so heavier shingles require more bundles per square.
It is the size of the roof! You need to measure the slope of each side of the roof by the length to come up with the sf of the roof. Most roofing is 4 bundles per 100 sf for dimensionals plus waste of about 20 to 30 per cent or 3 per square for regular shingles.
Convert 1,200 Square Feet to Square Inches
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