Multiply the length by the width (in feet) then multiply by 2 (for both sides) . THis will give you the square footage of the surface of the roof. Then divide that number by 100 ( the number of sq ft of shingles in one sq of shingles). Ex: 25' x 25' x 2 = 1250 sq feet. Divided by 100 = 12.5 sq of shingles.

One sq of shingles is three bundles.

One sq of shingles is three bundles.