# Sprayer Calibration Guide



## CarolinaCuttin (Sep 6, 2019)

I haven't seen any sort of information on the forums dealing with proper sprayer calibration, and it's such a simple but misunderstood topic so I figured I'd post a short write-up. I'm not sure if this belongs in the soil fertility section or not, but it was my best guess.

Most information you will get about sprayer calibration from YouTube videos generally recommend that you simply spray an area with a gallon of water and determine how much you were able to cover (or some variation of this principle). This is a decent way to grope towards the correct answer, but there is a much simpler method of sprayer calibration that can be done indoors with a calculator. It also allows you to fine tune these variables to your liking. The following equation will be your guide:

N = (V * S * W) / 5940

where

N = single nozzle output in gallons per minute
V = carrier volume in gallons per acre
S = speed in miles per hour
W = nozzle spacing (or fan width for backpack sprayers) in inches

It is very important to check the units when plugging in numbers. All of the variables are predefined with a certain unit that you must convert to before solving the equation. Let's run through a real life problem that I used to calibrate my sprayer

For the equation to be useful, you will need to plug in numbers for all but one variable, and then you can solve for the unknown. Suppose I want to figure out what my nozzle spacing needs to be in order to achieve a carrier volume of 50 GPA. I like 50 GPA because it is a happy medium between foliar and soil applications so I don't need to change nozzles all the time. I need to rearrange the equation so that I have the variable "W" all alone on one side. This gives:

W = (5940 * N) / (V * S)

I know my walking speed is 3 miles an hour because I have calibrated it previously to a metronome (see Walking Calibration below). I also know that my XR 110-04 TeeJet nozzle on my particular sprayer will spray 40 ounces per minute, or 0.3125 gallons per minute. Knowing this, I can plug in these numbers to get

W = (5940 * 0.3125) / (50 * 3) = 12.375 inches

This means that my nozzle spacing (fan width) needs to be 12.375 inches in order to achieve my target of 50 gallons per acre. In order to improve the accuracy of my applications, I double that number and try to have a fan width of 24.75 inches and overlap halfway into the previous pass. This will all but eliminate skips in your spraying. If you goof up on your spacing using this method, you will have still applied a half rate to the target area rather than a complete skip.

I'll post additional information at the bottom (such as walking calibration) and commonly asked questions as they come in. I hope this gives people a very accurate place to start spraying. Spraying to me is one of the most fun things about maintaining turfgrass, and doing it right is vital to protect your lawn, other people, and the environment. Good luck!

*Walking Calibration*

1. Choose your desired speed in miles per hour and convert to feet per second by using the following conversion factor:

1 mph = 1.47 ft/s

2. Next, multiply the speed in feet per second by 20 seconds, yielding a distance

3. Set your metronome setting to approximately 100 beats per minute and attempt to walk the distance calculated in step 2 in 20 seconds. Start timing when your sternum gets across the start line and stop timing when your sternum gets across the finish line. Your feet alternate between motion and no motion while walking, but your sternum should maintain a constant speed.

4. Adjust your metronome setting until you are walking the distance from step 2 in exactly 20 seconds. Do this multiple times to ensure accuracy.

*Writing Up Recipes*

Once you have your sprayer calibrated, you need a consistent method of writing up recipes so that you can mix correctly without confusion or mistake. Always determine your mixing order and product rates before mixing and according to all the labels of the products you are using. Always list your products in the order that they are to be mixed.

Example:

7/18/2020
Husqvarna Backpack Sprayer (50 GPA)
XR 110-04 (Red)
Tank = 1,100 square feet = 0.0253 Acres = 1.26 gallons = 161 fluid ounces

Soaker Plus @ 4 oz/M = 4.4 oz
Humic12 @ 6 oz/M = 6.6 oz
RGS @ 3 oz/M = 3.3 oz
Water = (161 - 4.4 - 6.6 - 3.3) = 146.7 oz


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## CenlaLowell (Apr 21, 2017)

Man that's some math for ya... I just use this

https://youtu.be/-U3yd0kxRR0


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## CarolinaCuttin (Sep 6, 2019)

@CenlaLowell They are using a method called the 1/128th method where you spray 1/128th of an acre so that ounces caught equals gallons per acre.

This is just a better variation of going out and spraying a given area and backing your way into the calibration. Since nozzle spacing is not fixed with a backpack sprayer it adds to the complication a bit. Lowering or raising the wand in space changes the fan width and therefore the carrier volume. Many people walk faster or slower during calibration than they will during application, so I'm a big fan of the metronome.

In any case, there are multiple ways to get the job done, and thanks for posting that video. I'm hoping this can be a place where we can collect resources for people that are looking to get into spraying. :thumbup:


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## g-man (Jun 15, 2017)

This is a great thread. This one and sprayer cleanup/PPE were in my long term list of articles to write. I like the metronome approach.

I learned a lot from this video when I started spraying. I don't use the poles but I do make sure I mow in a consistent pattern before spraying and use the mower stripes (~20in wide) to keep the spacing/overlap correct.

https://youtu.be/sYsSVAfEnTk


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## dwightevansjr71 (May 20, 2020)

CenlaLowell said:


> Man that's some math for ya... I just use this


Question? Lets say after you have done the calibration you come up with 16 gallons per acre like in the video. If you convert that to gal per/ksqft it comes out to .35 gal/ksqft. If I have 3 nozzles, doesn't this mean I am apply chemicals at about 1 gal/ksqft?


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## CenlaLowell (Apr 21, 2017)

No, it means your going to fast with the machine or you need bigger nozzles. Remember the goal in mind is to end up with 1 gal/1k so you test should have read 43 gal/1acre.


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## RVAGuy (Jul 27, 2020)

I feel like this is something that people make overly complicated. Get an electric backpack sprayer so your pressure is consistent. Get a nozzle for said sprayer (I use Teejet XR11004-VS for foliar applications and Teejet AIXR11004VP for pre emergent applications). Fun fact, the same colors for Teejets have similar flows at similar pressures, so you really don't need to calibrate twice unless you are anal.

The nozzles I use must be sprayed 20" high at 20" apart to allow overlap by design. The Teejet people know a lot more about spraying than any of us do and that's their suggestion for these nozzles. Spray 1,000ft² and see how much water is sprayed. Then mix whatever you are spraying, lets say, "X" Tablespoons/Oz/teaspoons per 1,000ft², into how many gallons of water you sprayed in 1,000ft², "Y". "X/Y" is now how much chemical you need to add per gallon.

One thing you must check with this method is some chemicals (Dimension 2EW for instance) require AT LEAST "Z" amount of water per 1,000ft²/Acre. Just check that. This way you don't have to **** around with trying to walk at THIS certain speed, calculate THIS specific nozzle, etc. This is essentially one big formula, and you are setting all the inputs and letting the amount of water to dilute be the output.


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## RVAGuy (Jul 27, 2020)

I would also like to mention doing a calculation as described in the original post would be ok for a tractor where you can set a speed (I assume as I'm not a farmer) and go from there. But spraying by hand with your exact setup is the most precise thing you can do. You can slow down if you need to to get the kind of coverage you feel is sufficient, or speed up. You may not be holding at the correct height the whole time, or the correct amount of overlap, etc. But all of this is accounted for with the 1,000ft² spray, so long as you are consistent.


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