Spray Characteristics 8: Spray Drop Size: The drop size is the size of the spray drops that make up the nozzle's spray pattern. The spray drops within a given spray are not all the same size. There are several ways to describe the drop sizes within a spray: (1) Sauter Mean Diameter (SMD) or D32: Fineness of spray expressed in terms of surface area produced by the spray. Diameter of a drop with the same volume-to-surface area ratio as the total volume of all the drops to the total surface area of all the drops. (2) Volume Median Diameter (VMD) DV0. 5 and Mass Median Diameter (MMD): Drop size expressed in terms of the volume of liquid sprayed. Drop size measured in terms of volume (or mass), with 50% of total volume of liquid sprayed drops with diameters larger than median value and 50% with smaller diameter. Drop sizes are stated in microns (micrometers). One micron equals 1/25,400 inch, or 0. 001 mm. One sixteenth (1/16) of an inch equals 1588 microns