Roofing nail quantity scales directly with the number of squares being covered, not with shingle bundle count alone, because nailing pattern (how many nails per shingle) can change based on the manufacturer's instructions and local wind-zone requirements. Standard 3-tab or architectural shingle installs typically use 4 nails per shingle at around 80 shingles per square, which works out to roughly 320 nails per square — high-wind zones may require 6 nails per shingle instead.

Once you know the total nail count, the calculation converts that into pounds using the nail count per pound (which depends on nail length and gauge), and then into full boxes based on the box size you're buying. Always round up to the nearest full box, and it's common practice to order slightly more than the exact math to cover dropped nails and touch-up work.