1. 1/128 Method Of Calibration Calibrating Hand Sprayers And High Pressure Hand Guns
Because a gallon = 128 ounces and the area to be sprayed is 1/128 of an acre, ounces collected = gallons per acre.
Calibration is knowing how much spray solution is going on a known area.
The one one hundred twenty eighth method is probably the easiest method of calibration to understand. There are other methods that work just as well and if you are comfortable with them by all means use them.
This method works because you are putting one ounce on 1/128 of an acre. This is the same as putting one gallon on one acre. However, it isn’t usually practical to spray an entire acre with small hand held equipment. We use 1/128 of an acre because it is a small area and application equipment can quickly and accurately be calibrated.
When you collect the output in ounces it equals gallons per acre.

2. Step 1
Measure out an area equal to 1/128th of an acre. Approximately 340 sq. ft. or an area 18.5 by 18.5 ft.
See slide. Remember an acre = 43,560 sq ft.
18.5 ft
18.5 ft

3. Step 1 Maybe this shape would work better. 10 ft 34 ft
The shape of the calibration course doesn’t have to be a square. It can be any shape you choose.
34 ft

4. Step 1
Or maybe this shape.
1.5 ft
See slide.
228 ft

5. The shape of the calibration course is not important.
However, the size of the course must equal 340 sq ft. or 128th of an acre.
See slide.

6. Step 2
Measure the time it takes to spray the measured area. Repeat several times and take the average time.
See slide.

7. Step 3
Spray into a container for the same amount of time it took to spray the measured area. Measure the water collected, in ounces. The amount collected in ounces equals gallons per acre.
See slide.

8. EXAMPLE Step 1. Measure area. 18.5 by 18.5 ft = 340 sq ft
HAND SPRAYER
Step 1. Measure area by 18.5 ft = 340 sq ft
Step 2. Time to spray = 51 seconds
Step 3. Amount collected = 40 ounces
Therefore; 40 ounces = 40 GPA
See slide.

9. Determining How Much Pesticide To Add To The Spray Mixture
Recommendation is to apply 1 quart of 2,4-D per acre
You get this information from the label. Always refer to the label as your final guide for pesticide rates and recommendations.

10. The sprayer is applying 40 gallons per acre
The sprayer is applying 40 gallons per acre. Therefore; You will need to add 1 quart of 2,4-D to each 40 gallons of water.
Your sprayer only holds 1 gallon of spray mixture. So how much pesticide will you need to add to the gallon of water?
See slide.

11. 1 quart or 32 ounces divided by 40 gallons means that each gallon of water contains 0.8 ounces of 2,4-D.
1 fluid ounce = 2 tablespoons. Therefore; You will need ~ 2 tablespoons of 2,4-D per gallon of water.
How do you measure 0.8 ounces. You can get close using a tablespoon.

12. 1 fluid ounce = 30 (cc) or (ml)
1 fluid ounce = 30 (cc) or (ml). Therefore; If measuring in cc you would need 0.8 ounces X 30 cc/ounce = 24 cc per gallon of water.
A plastic syringe is an easy and accurate way to measure liquid pesticides.
However, you can get more accuracy using a plastic syringe. They are available at most farm and ranch supply stores.
The best way to prepare your spray solution is to fill your sprayer about ½ full of water, then add the pesticide. Stir the spray solution and finish filling to the 1 gallon mark. You now have a solution that is ready to spray.

13. How large of an area will 1 gallon spray. There are 43,560 ft2/acre
How large of an area will 1 gallon spray? There are 43,560 ft2/acre. If 40 gallons will spray one acre then one gallon will spray an area 1/40 that size.
43,560 ft
= 1089 ft2.
Use the calibration information to help you plan your spray job. If you had a lawn to spray for dandelions that was about 2,000 sq ft in size then you know that you need at least 2 gallons of water and 1.6 ounces or 24 cc of 2,4-D.
An important thing to remember is that each person must calibrate hand held equipment. Not all people walk the same or spray the same.

14. 1/128 Method Of Calibration
MULTIPLE NOZZLE BOOM-TYPE SPRAYERS
This method of sprayer calibration gives sprayer output in gallons per acre when nozzle discharge is measured in ounces over a course length that = 1/128th of an acre or 340 ft2
The 1/128 method also works for large self propelled spray equipment.

15. Step 1
Adjust the sprayer pressure and check for uniformity. Operate the sprayer for 1 minute and measure spray from each nozzle. Clean or replace any nozzle that delivers + or - 5% than the output from a new nozzle in good condition.
See slide.

16. Step 2
Measure the spray band width or nozzle spacing in inches on the boom to determine the course length.
The area to be sprayed must equal 1/128th of an acre or 340 ft2
If the nozzle spacing = 20" then the distance to travel would be 204 ft.
See slide.

17. 20" (1.67 ft) X 204 ft = 340 ft2
204 ft
1.67 ft
340 ft2 or 1/128 of an acre
This is your calibration course. It usually works best if there are at least two people to help calibrate. One to drive the equipment and the other to time how long it takes to cover the calibration course. Remember to have the spray equipment up to speed before you reach the start line.

18. Step 3
Catch the spray from ONE nozzle while operating the sprayer under field conditions or for the time required to travel the needed distance at a desired speed.
See slide.

19. Step 4
Measure the spray collected in ounces. The number of ounces collected is the same as the number of gallons per acre.
See slide.

20. Example
You have a sprayer that has 15 nozzles on a 30 inch spacing. How would you calibrate it using the 1/128th method?
See slide.

21. Step 1
Make sure sprayer is adjusted properly and nozzles are in good working order.
See slide.

22. Step 2
Measure nozzle spacing in inches on the boom to determine the course length.
Using the formula:
4084 / 30 inches = 136 feet
Or from table 1. W = 30 inches and D = 136 feet
See slide.

23. Table 1. Distance (D) to travel and seconds required for selected speeds when nozzle coverage is (W) inches.
W (in)
D (ft)
2 mph
3 mph 20
204
70 seconds
46 seconds 24
170 58 39 26
157 54 36
Find 30 inch spacing on the table. You find that you need to travel 136 feet to equal 1/128 of an acre. At 2 mph it will take you 46 seconds to travel 136 feet and 31 seconds at 3 mph. 28
146 50 33 30
136 46 31

24. Step 3
Time how long it takes to travel the 136 ft at a desired speed. Travel this distance several times and get an average time.
Perhaps it takes an average of 31 seconds to travel the 136 feet.
See slide.

25. Step 4
Collect the spray from ONE nozzle in a container for 31 seconds.
Measure the water collected in ounces.
The amount collected in ounces equals gallons per acre.
If in 31 seconds you collected 20 ounces your sprayer output would be 20 gallons per acre.
If you collect 21 ounces why not adjust your speed so that the sprayer output is 20 ounces. Keep things in whole numbers. It make calculations much easier.

26. Determining How Much Pesticide To Add To The Spray Mixture
The recommendation from the label is to apply 1 quart of 2,4-D per acre.
See slide.

27. The sprayer is applying 20 gallons per acre.
Therefore; You will need to add 1 quart of 2,4-D to each 20 gallons of water.
See slide.

28. Your sprayer holds 200 gallons
Your sprayer holds 200 gallons. So how much pesticide will you need to add to the 200 gallon spray tank?
200 gallons divided by 1 qt 2,4-D per 20 gallons water = 10 quarts of 2,4-D per tank
See slide.

29. How large an area can be sprayed by your 200 gallon tank?
200 gallons divided by 20 gallons per acre = 10 acres
Calibration is not difficult and needs to be done on a regular basis. If you are spraying a lot you may want to calibrate your equipment every day.