A square of shingles is a standardized measurement used by contractors that applies to shingles of any size based on their ability to cover a certain area of roof.
Shingles and Roofing
Shingles are the building block of many roof styles, as contractors attach them to plywood sheathing to protect the roof from the elements.
A square is the number of shingles it would take to cover 100 square feet of roof area with each row of shingles covering the tabs of the layer below it.
Shingles are packaged in bundles that include a number of strips of roofing. Twenty-seven strips equal a bundle, generally speaking, and roughly three to four compose a square.
Shingle Size Issues
Since a square of shingles must cover the same amount of area, more shingles would be necessary if they were of a smaller size, and vice versa.
While a square is a square, the number of bundles it takes to have a square of shingles is dependent on the size of the shingles used and the construction of tabs to attach to the sheathing.