Square foot

[citation needed] It is defined as the area of a square with sides of 1 foot.

Although the pluralization is regular in the noun form, when used as an adjective, the singular is preferred.

[citation needed] This corresponds to common linguistic usage of foot.

[1] Dimensions are generally taken with a laser device, the latest in a long line of tools used to gauge the size of apartments[2] or other spaces.

Real estate agents often measure straight corner-to-corner, then deduct non-heated spaces, and add heated spaces whose footprints exceed the end-to-end measurement.