Surfactant Rate Per 100 Gallons Calculator
Size non-ionic surfactant for a spray batch from a quarts-per-100-gallons label rate and the total carrier volume, with per-tank and whole-field totals.
How This Calculation Works
Surfactant quarts equal the quarts-per-100-gallons rate times total carrier gallons, divided by 100. A 0.25 percent by-volume rate is the same as 1 quart per 100 gallons, and 0.5 percent is 2 quarts per 100 gallons. The total carrier comes from calibrated GPA times acres.
Field Calibration & Rate Reference Chart
| Ground speed | Nozzle pressure | Typical GPA | Droplet class |
|---|---|---|---|
| 4 mph | 20 psi | 12 | Coarse |
| 5 mph | 25 psi | 14 | Coarse |
| 6 mph | 30 psi | 15 | Medium |
| 7 mph | 35 psi | 16 | Medium |
| 8 mph | 40 psi | 18 | Medium |
| 9 mph | 45 psi | 19 | Fine |
| 10 mph | 50 psi | 20 | Fine |
| 12 mph | 55 psi | 22 | Fine |
| 14 mph | 60 psi | 24 | Very fine |
| 16 mph | 65 psi | 26 | Very fine |
Common Questions
How do I convert a percent-by-volume surfactant rate to quarts per 100 gallons?
One percent of 100 gallons is 1 gallon, which is 4 quarts. So 0.25 percent equals 1 quart per 100 gallons and 0.5 percent equals 2 quarts per 100 gallons. Multiply the percentage by 4 to get quarts per 100 gallons directly.
Does surfactant rate change with carrier volume?
Yes. The label rate is expressed per 100 gallons of spray mix, so a higher GPA means more surfactant for the same acres. Recalculate whenever you change carrier volume, or you will under-dose a high-volume pass and lose coverage.
When should I use a crop-oil concentrate instead of non-ionic surfactant?
Crop-oil concentrate is often specified for grass herbicides and for products that need slower droplet drying and better penetration of waxy leaf surfaces. Non-ionic surfactant is the default for most broadleaf herbicides. Always follow the product label, because the wrong adjuvant can reduce control or injure the crop.
Does hard water affect surfactant performance?
Hard water can tie up some herbicide actives and reduce surfactant efficiency, especially with glyphosate. Adding ammonium sulfate at the labeled rate conditions the water before the surfactant goes in. Test your water source once so you know whether conditioning is needed.