Vacuum has two measurable properties, its negative pressure, or pressure differential, and volumetric flow. Vacuum Pressure or the pressure exerted by a denser outside atmosphere, is measured in a variety of units. Vac Cubes uses “hg, inches of mercury, as our standard unit although bar, torr (mmhg) and % vacuum are also commonly used. Vac Cubes uses CFM, as our unit of volumetric flow, other common units include m3/h and l/m. CFM is the number of cubic feet of air moved through a cross section in a minute.