In FM standards, uplift loads are commonly measured in which unit?

• A. Newtons per square meter
• B. Pounds per square foot (psf)
• C. Pounds per square inch
• D. Kilopascals

Answer: (B)

Uplift loads on roofs are pressures expressed as force per area, and in FM standards the common way this is shown is in pounds per square foot. This unit fits the way roofing assemblies are designed and documented in the U.S.—tables of uplift resistance, fastening requirements, and membrane details are all aligned to psf so designers can gauge performance per each square foot of roof. If you need a quick sense of scale, 1 psf is 1/144 of a psi and about 47.9 Pa, so you can convert to metric units if needed, but psf remains the standard in FM and typical U.S. roofing practice because it mirrors how roofs are sized and rated in the field. The other options are metric or more granular pressure units that aren’t the conventional choice for roof uplift in these standards.