Applying a herbicide on your lawn safely and effectively requires reading the label. The first time you thumb through the pages, you may come across the term gallons per acre.
It’s a simple concept, but what does gallons per acre really mean? Understanding it is key to accurate, effective, and safe chemical application. Whether you’re applying herbicides, insecticides, fungicides, or fertilizers, knowing your gallons per acre (GPA) helps ensure that you’re applying the right amount of product, using the right amount of water or carrier, and getting proper coverage across the target area.
Let’s break it down.
Gallons Per Acre = Application Rate
Gallons per acre (GPA) refers to how much total spray solution (water + chemical) is applied to one acre of land. The right GPA rate for you will depend on several factors. You can read more about determining your GPA rate in this article, but the GPA is often determined by the type of sprayer you have.
Identifying the appropriate GPA rate is just half the battle. The total volume of liquid applied per acre is important, however, it may not be vital. Some chemicals will provide specific GPA requirements, others will provide more general guidelines.
More water mixed with a pesticide or fertilizer can help the product to be effective and safer for use. Ultimately, for many chemicals, it is the actual amount of pesticide, fertilizer, etc., that is getting applied per acre that is the most important factor.
You see, a sprayer will disperse a certain amount of liquid within a given amount of time. This amount is dependent upon the operating pressure of the sprayer and the size of the nozzles on the sprayer boom or the spray gun.
When you spray, the sprayer or spray gun is being moved, it is not standing still. So the speed at which the sprayer is traveling will also affect the GPA rate. Furthermore, if it is a boom sprayer, the spacing between the nozzles also affects the volume of liquid applied per acre.
Nozzles closer together mean the sprayer is delivering a greater volume of liquid in a given area versus a sprayer going the same speed at the same pressure with the same size nozzles.
GPA vs. Chemical Rate: What’s the Difference?
Here’s where it gets a little confusing—but stick with me. Your GPA is your spray volume—how much liquid you’re laying down per acre. Your chemical rate is how much of the actual product (herbicide, pesticide, etc.) you need per acre.
Make sense yet? Either way, let’s look at a real-world example. Drive XLR8 is a herbicide that is used to target crabgrass. The label provides pretty specific directions for broadcast applications with boom sprayers.
GPA Application Rate:
“Apply with properly calibrated ground equipment in sufficient water per acre to provide uniform spray distribution (at least 20 gallons of water per acre or at least 0.5 gallon per 1000 square feet). Use low-pressure sprayers at 20 to 40 psi.”
Chamical Rate:
“64 fl ozs of product per acre or 1.45 fl ozs per 1000 sq ft”
–Drive XLR8 Label
What this means:
1. Herbicide Rate (How much product to use)
You have two equivalent ways to express the rate:
- Per acre: 64 fluid ounces (fl oz) per acre
- Per 1,000 square feet: 1.45 fl oz per 1,000 sq ft
These are the same rate, just adjusted for area size.
2. Carrier Volume (How much water to mix it with)
The label says:
- Use at least 20 gallons of water per acre
- Or at least 0.5 gallon per 1,000 sq ft
This is your spray volume, also called carrier volume. It’s how much total spray mix you’re applying to the area (herbicide + water).
3. Mixing Example (Per 1,000 sq ft)
To treat 1,000 square feet, the label tells you to:
- Use 1.45 fl oz of Drive XLR8
- Mix it into at least 0.5 gallons of water
- Spray the entire 0.5 gallon evenly over 1,000 sq ft
4. Mixing Example (Per Acre)
To treat 1 acre (43,560 sq ft):
- Use 64 fl oz of Drive XLR8
- Mix into at least 20 gallons of water
- Spray the entire 20 gallons evenly over 1 acre
- You must apply 64 oz of chemical per acre.
- But that 64 oz needs to be diluted in 20 gallons of total liquid.
- Your sprayer needs to be calibrated to output that amount evenly across the entire acre.
Let’s Look at a Specific Example
In this example, we’re using a typical boom sprayer with the following specifications:
- Tank Size: 50 gallons
- Boom Configuration: 7 nozzles spaced 20 inches apart
- Nozzle Flow Rate: 0.34 gallons per minute (GPM) at 29 psi (Red 04 size nozzle that puts out 0.4 GPM at 40 PSI, but we need lower PSI to achieve 20 GPA rate on this sprayer. Learn more here.)
- Spraying Speed: 5 miles per hour (mph)
The goal is to apply Drive XLR8 herbicide at the label rate:
- 64 fluid ounces per acre, with a minimum of 20 gallons of water per acre.
Determine Your Application Rate (Gallons per Acre)
I know that this sprayer is already setup to apply 20 GPA at 5 mph based on the nozzle spacing and nozzle size, but if your sprayer differs, you will need to determine nozzle size based on your sprayers nozzle spacing, your desired travel speed, and the GPA rate (in this case 20GPA). Learn more about sizing nozzles here.
How Many Acres Can You Cover Per Tank?
Next, divide your tank size by your GPA to find how many acres each tank will treat. Pretty simple in this case, 50 gallon capacity divided by 20. So, your 50-gallon sprayer will cover about 2.5 acres per full tank.
Step 3: How Much Drive XLR8 to Add?
According to the label, Drive XLR8 should be applied at 64 fl oz per acre. Multiply this by the number of acres your tank covers: 64 fl oz/acre×2.5 acres=160 fl oz. That’s 1.25 gallons of herbicide per 50-gallon tank.
Final Mix Summary
| Parameter | Value |
|---|---|
| Spray Volume (GPA) | 20 gallons per acre |
| Area per Tank | 2.5 acres |
| Drive XLR8 per Tank | 164 fl oz (1.25 gal) |
| Sprayer Speed | 5 mph |
| Boom Width | 120 inches (10 ft) |
| Nozzle Flow Rate | 0.34 GPM @ 29 psi |
| Nozzle Spacing | 20 inches |
Tips for Adjusting Your Application
If you want to apply more acres per tank or reduce your water usage:
- Increase speed (MPH)
- Use nozzles with lower flow rates (GPM)
- Widen nozzle spacing (if agronomically acceptable)
Just remember: if you change anything about your setup, recalculate your GPA to make sure you’re still meeting label requirements.
Why GPA Matters So Much
Spray coverage isn’t just about getting the chemical on the plant or pest—it’s about getting it there uniformly and at the correct concentration.
Using the wrong GPA can lead to:
- Poor results (weeds not dying, pests surviving)
- Wasted product (more cost, more tank refills)
- Environmental risk (overapplication or runoff)
Calibrating for the Right GPA
We’ve got a full guide on how to calibrate your sprayer, but the big idea is to make sure your sprayer is delivering the exact amount of liquid across the acreage you’re treating.
Final Thoughts
Gallons per acre is the foundation of good spray application. Understanding it ensures you’re applying the right amount of chemical, saving time, protecting your crops or turf, and staying within label guidelines. Need help figuring out your actual output or selecting the right nozzles to hit a certain GPA? Sprayer Guru is here to help.
More Beginner Sprayer Calibration Info:
