How to calculate it yourself
Squares = total roof area in ft² ÷ 100. Always order by the square (rounded up), not by the bundle, to avoid dye-lot mismatches if you run short mid-job.
Common scenarios
Replacing a 1,800 ft² roof
1,800 ÷ 100 = 18 squares. Add 10% waste = 20 squares. That is 60 bundles of 3-tab shingles or 80 of architectural.
Pricing labor by the square
A re-roof in the US averages $350–$550 per square installed (materials + labor + tear-off). A 25-square house is $8,750–$13,750.
Calculating from footprint and pitch
A 30×40 ft footprint with a 5/12 pitch has a roof area of 1,300 ft² ÷ 100 = 13 squares. Use a roof pitch calculator to convert footprint to roof area.