Spray Droplet Density & Coverage on the Leaf

It is the number of spray droplets that land on each square centimetre of leaf. Good coverage needs enough droplets per cm² so the active reaches its target; too few leaves gaps where pests or disease survive. This tool estimates droplets/cm² from your spray volume and droplet size and rates the coverage.

Each droplet has a volume from its diameter (a 250-micron droplet is far larger than a 100-micron one). The spray volume per area divided by the volume of one droplet gives the number of droplets per area, which converts to droplets per cm². Smaller droplets pack many more per litre, so density rises sharply as droplet size falls.

Droplet volume scales with the cube of diameter, so halving the droplet size makes each droplet eight times smaller — meaning eight times as many droplets from the same litre of spray. That is why fine sprays give high droplet density and excellent coverage, at the cost of much greater drift risk.

Fine droplets give more droplets per litre and better coverage but drift far more in wind and evaporate quickly. Coarse droplets resist drift and reach the canopy reliably but cover less per litre. The right choice balances the coverage a product needs against the drift conditions on the day.

It depends on the product. Contact pesticides and fungicides that must hit the target directly need high density — often 50–70+ droplets/cm². Systemic products that move within the plant tolerate lower density. The coverage class here flags whether your settings are likely sparse, adequate or dense for the job.

Droplet size is set mainly by nozzle type and spray pressure: finer nozzles and higher pressure give smaller droplets and more drift; air-induction or larger nozzles and lower pressure give coarser, drift-resistant droplets. Nozzle catalogues quote a volume median diameter (VMD) you can enter here.

Yes — for a given droplet size, more litres per area means more droplets per cm². But raising volume to fix coverage eventually causes run-off, wasting product. Often it is smarter to choose a droplet size that gives the density you need at a sensible volume than to simply pour on more water.

By showing the droplets/cm² your settings actually deliver, you can choose the coarsest droplet that still gives adequate coverage — getting the deposit you need while keeping droplets large enough to resist drift. That protects neighbouring crops and waterways and keeps more product on target.

They are solid planning figures. Real deposition varies with droplet spectrum, leaf angle and waxiness, canopy density, evaporation and spray dynamics. Use water-sensitive papers in the field to check actual density, and treat these numbers as a guide to set up the spray rather than an exact measurement.