How do I figure out how much hardwood to purchase?

Most flooring is priced by the square foot but is sold by the box.
The square footage is the actual measurement of the area to be covered by flooring. A waste factor of 5% must be added to the amount of square footage of flooring needed to allow for cutting waste.
Example:  10′ x 15′ room
10’x 15’ = 150 sq. ft.
5% x 150 sq. ft. = 7.5 sq. ft. = 8 sq ft
Total sq. ft needed = 158 sq. ft.
Sq. ft. per box = 18 sq. ft.
158/18 = 8.8 = 9 boxes
Number of boxes purchased = 9 boxes
The cutting waste also allows for some minor defects if any in the wood to be cut out.