See the calculation with sample numbers
A 300 sq ft net floor with 10% extra needs 330 sq ft. At 21.5 sq ft per box, that is 16 whole boxes covering 344 sq ft.
What can change the result?
Confirm box coverage, batch or lot requirements, and installation waste with the flooring manufacturer.
How this was calculated: Order area, whole boxes, purchased coverage, waste and rough materials cost.