The droplet spectrum

All agricultural nozzles produce a range of droplet sizes. This is a useful feature as the crops to be sprayed always present a 3-dimensional target with contrasting leaf surfaces and angles. In a dense crop, for example, finer droplets are likely to be deposited on the top leaves and larger droplets lower down.

Droplet sizes are measured in microns.
1 micron is 1/1,000,000 m or 1/1,000 mm

To describe the median droplet sizes produced from a specific nozzle, the term VMD is used.

VMD = Volume Median Diameter
VMD is the drop dimension where the accumulated volume of smaller droplets accounts for 50% of the liquid leaving the nozzle; and all larger droplets account for the remaining 50% of total volume.

Wind drift is generally regarded to be mostly caused by droplets below 150 micron in diameter.