How many squares would you install when replacing the roof of 1578 sft with 3-tab shingles?

When talking about the area of a roof, remember that it is not the same as the square footage of the structure. For example a 20 x 30' building with a 12" overhang and a 4/12 pitch will have 736 sq ft of roof vs only 600 sq ft of slab.

One square of shingles covers 100 square feet. 15 year shingles come 3 bundles to a square. 25 year come 4 bundles to a square.