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How do you calculate the required amount of spray liquid?

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Written by Jan-Paul de Wit| Last update: 07-04-2021

To limit the amount of residual liquid as much as possible when spraying, it is important to calculate the required amount of spray liquid as accurately as possible. Limiting residual liquid is not only better for the environment, but it also saves money on an annual basis because less crop protection product is wasted. We explain how you can calculate the required amount of spray liquid as accurately as possible. 


A crop protection product must be dosed in a specific way. The dosage is the amount of crop protection product per unit (square meter or hectare) that should be applied to the crop for the best effect. This can be indicated in liters or kilograms. The dosage is indicated on the product label. This can be expressed per plant, per pot or per hectare. 


For some applications, it is not possible to indicate the amount of product needed per hectare, for example because the size of the crop changes significantly during cultivation, or because the product is intended for spot spraying. In these cases, the concentration (also called the mixing ratio) of the spray liquid is indicated on the label. You can use this to calculate how much spray liquid you need to prepare per unit area. 

Calculate amount of spray liquid

To calculate the required amount of spray liquid, you need to follow three steps:
  • Calculate area: first you need to calculate how big the area is that you want to spray. The rule is: area = length x width.
  • Calculate the amount of water: the amount of water you need depends on the spray nozzle you use. The amount of water needed per hectare when using a particular spray nozzle can be read from a nozzle table.
  • Calculate the amount of crop protection product: you can calculate this when you know how much water you want to use (step 2) and what the concentration of the crop protection product to be used is. Divide the amount of water from step 2 by 100. Now you know what 1% of the required amount of water is. Multiply this by the percentage of crop protection product you need to add to the water. The result is the required quantity of crop protection product in liters.

Calculation example

  • The greenhouse has a surface area of 320 m x 112 m = 35,840 m².
  • The nozzle you want to use sprays 627 liters per Ha.
  • The concentration of the crop protection product to be used is 0.025%, or 25 milliliters per 100 liters of water. 1% of the water required is 627 : 100 = 6.27. So the required amount of crop protection product in liters is 0.025 x 6.27 = 0.157 liters.

More information about calculating the amount of spray liquid

Do you have questions about the amount of spray liquid, or would you like tailored advice? Please contact crop protection specialist Jan-Paul de Wit via the form below. You will receive a response as soon as possible, on weekdays even within 24 hours.

Jan-PaulAbout Jan-Paul de Wit

Jan-Paul de Wit is specialist in Integrated Pest Management. He helps and advices growers on how to improve their crops and how to fight diseases, viruses and pests. He advises on the best products to use so that they optimally match the objectives of the grower, as well as the crop, greenhouse and environment.

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