square foot

The square foot prices American buildings. Homes are listed, appraised and compared by it, offices are leased by it, and construction costs are estimated per square foot before any drawing exists. The handiest anchors come from the materials themselves: a 4 by 8 ft sheet of plywood or drywall is exactly 32 sq ft, a two-car garage runs around 400 sq ft, and a standard parking stall about 160 sq ft.

Roofers trade in a unit built on top of it: the "square", exactly 100 sq ft of roof coverage, so a 2,400 sq ft roof is a 24-square job and shingles are bundled and priced per square. The trap for engineers is that the US R-value carries the square foot inside it. R-13 insulation means 13 ft²·°F·h/Btu, and dividing by 5.678 gives the metric RSI value, so American and metric R-values for identical insulation differ by a factor near six, a mismatch that surfaces whenever a US spec meets a metric heat-loss calculation like the ones this site runs. The caution above about gross, rentable and usable area is the other place square-foot numbers quietly diverge, and it is where the money moves.