Friday, September 29, 2023
HomeLawn CareDIY Lawn Care: Sprayer Calibration Process

DIY Lawn Care: Sprayer Calibration Process

We did a basic DIY Lawn Care video last year. We received a lot of questions about how we calibrated our pull-type sprayer before spraying the weed killer and herbicide. So we decided to video our calibration process this year. We’re not lawn care experts, just home owners who want to take care of our own property. We paid Tru-Green for several years to take care of our lawn. They were not perfect either. We saw areas of our yard that were missed or places the grass was killed. After buying Johnny, we decided to give it a try ourselves.  Here is a link to last year’s post and videos 2016 DIY Lawn Care Info and Videos

We purchased an economical 15 gallon sprayer at Rural King. This was not the most expensive sprayer but it works for the few times a year we need it. This sprayer can run on 12 volts, is rated at 84″ spray coverage, has an 18″ handgun with 15 foot of hose, an adjustable pressure with return to the tank and is glyphosate compatible. All this for under $200.00! The handgun is nice to keep up on the tractor when we want to stop and spray targeted areas without getting off Johnny. It will run up to 60 psi but for spraying lawn chemicals, we run it at approximately 25 psi.

Each year, we check the hoses and spray tips for any signs of problems like cracking (they are plastic after all) or missing parts. We clean the spray tips and strainers before rinsing and filling the tank with water.  This year, we  took the sprayer to our driveway where we could see the spray pattern. We turned on the sprayer and allowed it to run for a couple of minutes. At this point, we were be able to detect any  abnormalities with the spray nozzles themselves.  When we saw the spray pattern, we realized it was wider than the 84 inch rating. We measured the actual width to be approximately 10 feet.

Calibration Process:

Step 1: Calibration Course

For ease of calculations, we decided to use 1000 sq. foot as the area for the calibration course. Therefore, we needed to calculate the distance to drive Johnny to equal 1000 sq. ft. Since the total width of our spray pattern was 10 ft, the length of the course was easy to calculate! 1,000 sq ft/10 ft = 100 ft.

We marked out a course in our backyard that was 100 sq. ft long. You need to do this on your lawn – not a driveway or hard surface. We used orange spray paint to mark the beginning and ending point but you could easily use flags, cones or other markers (children, stuff animals, neighbors, etc).

While Johnny is great, he doesn’t have a speed-odometer. So we couldn’t drive him at a specific mph.  To be consistent, Tim decided to set the RPM to 2000, use low gear and press the foot petal all the way down.

It is recommended to drive between 3 – 4 mph for those of you with speed odometers on your rig.

For the remainder of this process, you will need a partner – wife, child, neighbor, even a teenager will do.

We then recorded the amount of time it took Johnny to complete the 100 foot linear course 4 times. Repeating the course multiple times help improve your accuracy. It’s a little boring but hey your yard deserves a little love.

It took Johnny over 28 seconds to complete the course one time (remember low gear! – this isn’t a race).

113.27 seconds is the amount of time to cover 4000 sq. ft. That will be important in the next step!

It was a nice evening and Johnny was enjoying the attention. However, we soon realized that this was taking more time than we had anticipated. You might want to do this on a Saturday morning when you have plenty of time. We have been so busy lately that every minute is planned. This was the only time we had – and the dandelions were getting huge!

Step 2: Determine the Flow Rate of the Spray Tips

Collect the amount of water from both tips for the amount of time in seconds recorded in Step 2. We used a 5 gallon bucket under each of the 2 tips. Tim turned on the water and counted down so that I could start the timer exactly when he started the sprayer. We allowed the water to spray into the buckets until ~113 seconds elapsed. We combined the water collected into 1 bucket. This was the total amount of water that would have been sprayed over 4000 sq. feet of yard.

We then measured the amount of water in the bucket and divided it by 4 to give us the exact amount of gallons per 1000 sq ft.

We used a simple plastic measuring container purchased at Menards. I didn’t want to use any measuring cups from my kitchen since there might be residual chemicals from the tank.

In summary for our calibration process, the output of our two-nozzle boom pull-type sprayer at an operating RPM of 2000, in low gear, with the foot petal all the down, and the sprayer at 25 psi, is 0.36 gal. per 1,000 sq. foot.

Step 3: Determine The Area to Cover

Measure or approximate the amount of area in sq feet for the grassy part of your yard. Remember to subtract buildings, driveways and other large areas that will not be sprayed. We subtracted our house, Johnny’s shed, the driveway, and our 2 garden areas leaving us with approximately 14,000 sq feet of grassy area (well, weedy areas before spraying).

Then divide the total sq ft by 1000 and multiply by the total output of your sprayer from Step 2.

For us, we needed to add 5.04 gallons of water minus the amount of chemical recommended per the product label directions to spray our 14,000 sq foot yard.

By this time it was getting dark. We quickly added the calculated amount of water and chemicals to our sprayer and Tim got to the business of killing weeds and preventing crabgrass. We’ll post another blog about the chemicals we used. Just keep in mind that there is a lot of choice for chemicals depending on your grass type and weeds common to your yard. Please research the best chemicals to treat your lawn!

For now, grab some popcorn and enjoy our DIY Sprayer Calibration video:

The sprayer should be rinsed well after each application due to build up of fertilizers and pesticide residues. Read labels carefully and apply according to the directions and pesticide laws.

Don’t hesitate to leave us a comment.  How do YOU handle the sprayer calibration issue?



  1. My 2 nozzle sprayer at 25 psi for 28 seconds sprayed 73 ounces of water, quite a bit more than yours, do i just use that as my calibration measurement and go from there

  2. Chapin recently brought out a Mixes-on-Exit sprayer that uses a clean water tank and a separate changeable chemical tank. Your main water tank can stay clean of chemicals provided you disconnect the chemical tank when not in use, else there is a chance it could drain back to the water tank. With multiple chemical tanks you can keep your Live (fertilizers), Die (weed and bug killers), and Live and Let Die (weed and feed) from contaminating each other. Yes, sometimes treating lawn, garden, and fruit trees does feel like a Bond mission.
    I got the 25 gallon UTV mount version with hand spray and temporarily mounted it on some lumber over my ballast bucket on the 1025R. I also got the two-nozzle spray boom much like what Tim is using. The 3-pt now gives me some height control along with the boom mount position and that height has a big effect on the spray coverage area. Chapin claims a seven foot width when the nozzles are at the correct height for the two nozzle patterns to meet without excessive overlap. It was easy to set up over the driveway. The bar comes with two sets of nozzles, green low range up to .45 gph at 30 psi, and blue high range up to .83 gph at 30 psi, both are per nozzle so double that for total flow. There is a 12VDC pump that pulls from both tanks through a mix rate control. The wiring comes for connection to the battery but I adapted it to the 12V power outlet on the right fender. It has an on off switch that can be used from the seat. The mix rate has various setting but it seems rarely the one I happen to need. I just premix in the chemical tank to dilute enough to use a higher mix rate.
    I used a GPS device that will show speed in tenths to check Johnny for mph at various RPM at low range full pedal. Lots of spreadsheet work let me convert the needed pounds per acre to a speed with the chemical dilution and mix rate selected.
    Now I only need a brief rinse through the spray lines after each chemical and can quickly move to another if needed. The chemical tank is easy to see over my shoulder so I don’t run out and just water the weeds.

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