University Of Illinois Introduces New Spray App

University of Illinois Extension has released a new smartphone app for making sprayer-related calculations. Pesticide Spray Calculator, or Spray Calc, is available for both Apple and Android smartphone platforms. It contains multiple functions related to calibrating a sprayer.

University of Illinois Spray Calc AppThe opening screen allows the user to select from one of four main options:

  1. Calibration: allows user to calibrate four different sprayers types.
  2. PSI for GPM: allows user to calculate required pressure in order to provide a specific flow rate, or do the opposite.
  3. Nozzle Speed: determine minimum and maximum speeds for a specific nozzle.
  4. Convert Value: various pesticide application related unit conversions.

Throughout the app, help menus are available to provide guidance as to the function of various app components, as well as definitions for many of the variables listed. For most variables, touching the name of the variable brings up a definition of what the variable is and how it is measured.

Selecting “Calibration” leads to a screen with four options: Aircraft, Ground Rig, Turf Boom, and Boomless. Within each section, calibration scenarios can be saved for future reference and for values to be loaded into some of the other functions available on the app. Each option will be discussed separately.

Aircraft Calibration

The aircraft option has two different screens. The first screen allows the user to enter their speed in miles per hour, desired swath width in feet, the GPA (gallons per acre) of spray to be applied, and the total number of nozzles on the boom. The required flow rate for the boom is calculated, as well as the required flow rate for each individual nozzle. The user can save the entered values with a name of their choice, and, if so desired, slide to the second aircraft calibration screen for more calibration options.

The second aircraft calibration screen allows the user to fine-tune number of nozzles, orifice size, and operating pressure in order to achieve the required boom GPM flow rate. It also allows the user to use up to two different orifice sizes on the boom in order to achieve the required boom GPM. The needed boom GPM from the first screen is carried over from the first screen.

Users can the select how many different orifice sizes they want on the boom (one or two) and the operating pressure (psi or pounds per square inch) they want to operate at. For each orifice size, they need to enter the flow rate provided by that orifice size at 40 psi (example: a 4010 flat fan nozzle provides 1.0 GPM at 40 psi) and the number of nozzles with that orifice size. The app will calculate the total GPM for all nozzles of that size, as well as the total for the entire boom. If only one orifice size is used, the total for nozzles and boom total will be the same. The user can change any of the variables until the boom total at the bottom matches the needed boom GPM at the top.

Ground Rig Calibration

This function consists of a single screen and can be used to calibrate a ground rig sprayer. The user enters the speed at which the application will be made in miles per hour, the nozzle spacing in inches, and the targeted GPA. The app calculates the required nozzle flow rate in gallons per minute. Similar to the aerial function, each application scenario can be saved with a user-determined name for future reference and use in other app functions.

Turf Boom Calibration

The turf boom function is identical to the ground rig function except that the spray application rate is entered as gallons of spray per 1,000 square feet instead of gallons per acre. This function can be used to calibrate boom sprayers used to make broadcast applications to turf with products labeled using spray application rates in gallons per 1,000 square feet. Each application scenario can be saved with a user-determined name for future reference and use in other app functions.

Boomless Calibration

The boomless function is identical to the ground rig function except that swath width in feet is entered instead of nozzle spacing in inches. This function can be used to calibrate sprayers set up with off-center type nozzles that are typically used to make applications to rights-of-way areas and pastures. Each application scenario can be saved with a user-determined name for future reference and use in other app functions.


This function allows the user to do one of two things. The first is to calculate the required pressure at which to operate a nozzle in order to achieve a specific flow rate. This can occur when the required flow rate for an application is not specifically listed in a nozzle manufacturer’s flow rate table. To make this calculation, the user needs to know a flow rate and associated psi. This is easily determined by the name of the nozzle. For example, an XR11004 is an extended-range nozzle (XR) with a 110-degree spray angle. The last two digits provide the flow rate for the nozzle at 40 psi by placing a decimal point between them: 0.4 GPM. So if you wanted to use a XR11004 nozzle to provide a 0.36 GPM flow rate, you would need to operate it at 32.4 psi.

Another way to use the PSI for GPM function would be if an applicator wanted to operate a nozzle at a specific pressure. This might occur in order to create a droplet spectrum required by a label. As with the previous usage, users must enter a known flow rate and pressure for the nozzle. They then enter the psi at which they wish to operate the nozzle and the app will calculate the GPM generated by the nozzle at that pressure.

Nozzle Speed

This function can be used to determine the maximum and minimum speeds at which a nozzle should be operated. It should be used when an applicator has a sprayer equipped with a flow control system. Flow control systems automatically maintain an applicator-selected spray application rate. They do so, however, by adjusting pressure. As a sprayer is operated faster, nozzle flow rate must be increased in order to maintain the set GPA. Unless the sprayer is outfitted with a pulse width modulation control system, the flow controller has to increase pressure in order to increase flow rate. A similar thing happens when the sprayer slows down – pressure is reduced to reduce nozzle flow rate so that the GPA is maintained.

The factor limiting the speed range of the sprayer, therefore, is the operating pressure range for the nozzle. The nozzle speed function is used to calculate the sprayer speeds that correspond with the upper and lower pressure limits of the nozzle. The applicator enters the nozzle spacing and the targeted GPA. Next, the applicator refers to the flow rate table for the nozzle that will be used; GPM min operating pressure is the nozzle flow rate in GPM when the nozzle is operated at its lowest pressure; GPM max operating pressure is the nozzle flow rate in GPM when the nozzle is operated at its highest pressure.

For an XR110004, the minimum pressure is 15 PSI and the maximum pressure is 60 PSI. At 15 PSI, the flow rate is 0.24 GPM; at 60 PSI the flow is 0.49 GPM. When these values are entered into the nozzle speed function, the app calculates the minimum operating speed as 7.13 MPH and the maximum operating speed is 14.55 MPH. Keeping the sprayer within this speed range will ensure the nozzle is operated within its pressure operating range. It will not, however, prevent the droplet spectrum from changing. As can be noted in figure 6, an XR110004 will produce a medium (M) droplet spectrum at 15 PSI, but it will change to a fine (F) droplet spectrum at 60 PSI.

Convert Value

The convert value function allows the user to convert various values commonly associated with pesticide applications. The list of values that can be converted is by no means exhaustive and will likely be expanded as the app is updated. The top section of the convert value screen allows the user to select the type of values to be converted. These include flow rates, spray rates, rate conversions for volume per unit area, weight per unit area, and weight per volume.

Once the user has selected the type of value they wish to convert, they select the unit they wish to convert from and the unit the wish to convert to.


Spray Calc was created to assist applicators with many of the calculations used to calibrate and set up a sprayer. In the future, functions to assist with tank mix calculations will be added along with other possible functions. If you have any questions or suggestions about Spray Calc, please contact Scott Bretthauer at

Spray Calc is available in iTunes and the Google Play store.



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