For specific choices of duct material, and assuming air at standard temperature and pressure (STP), standard charts can be used to calculate the expected friction loss. The chart exhibited in this section can be used to graphically determine the required diameter of duct to be installed in an application where the volume of flow is determined and where the goal is to keep the pressure loss per unit length of duct "S" below some target value in all portions of the system under study. First, select the desired pressure loss Δ"p" / "L", say 1 kg / m2 / s2 (0.12 in H2O per 100 ft) on the vertical axis (ordinate). Next scan horizontally to the needed flow volume "Q", say 1 m3 / s (2000 cfm): the choice of duct with diameter "D" = 0.5 m (20 in.) will result in a pressure loss rate Δ"p" / "L" less than the target value. Note in passing that selecting a duct with diameter "D" = 0.6 m (24 in.) will result in a loss Δ"p" / "L" of 0.02 kg / m2 / s2 (0.02 in H2O per 100 ft), illustrating the great gains in blower efficiency to be achieved by using modestly larger ducts.