Nozzle Pressure Calculator

Use this Nozzle Pressure Calculator to find the PSI (or bar) you need to hit your target gallons per acre. Enter your rate, speed, nozzle/row spacing, and your nozzle’s rated flow/pressure to get the required pressure and per-nozzle flow. Then verify pattern and droplet size class on your nozzle chart (see: What Do the Numbers on a Sprayer Nozzle Mean?)

How to Use This Nozzle Pressure Calculator

1. Enter Target Rate (GPA), Travel Speed (mph ), and Nozzle/Row Spacing (in).
2. Select a common nozzle size or type your nozzle’s rated flow and its rating pressure (e.g., 0.40 GPM @ 40 PSI. If you don’t know your nozzle size, read this guide for help.
3. Review the Required Pressure output. If PSI is outside your preferred range, the tool suggests a swap to a smaller or larger ISO size to bring pressure back toward mid-band.
4. Confirm droplet size class and pattern on your nozzle chart. Learn more about this in my beginner guide to sprayer nozzle charts.

What the Calculator Does

• Converts your target GPA, speed, and spacing into the flow each nozzle must deliver.
• Uses the standard orifice relationship to compute the pressure you need with your chosen nozzle: P₂ = P₁ × (Q₂ / Q₁)².
• Detects the nearest ISO nozzle size and shows the standard color code so you can match what’s on your boom.
• Suggests an upsize/downsize if your required PSI is too low (poor pattern risk) or too high (wear/drift risk).

What If My Required PSI Is Too Low or Too High?

• PSI too low (often <20 PSI): pattern quality can suffer. Try a smaller nozzle (lower ISO number) or increase ground speed.
• PSI too high (often >60–70 PSI): drift risk increases. Try a larger nozzle (higher ISO number) or slow down.
• Mid-band target: many non-AI flat-fans perform well near ~40 PSI—always confirm on the chart for your exact nozzle and application.

Example

Target: 15 GPA, 10 mph, 20″ spacing, using a 0.40 GPM @ 40 PSI nozzle.
• Per-nozzle flow = 15 × 10 × 20 ÷ 5940 = 0.505 GPM.
• Required pressure = 40 × (0.505 ÷ 0.40)² ≈ 63.8 PSI.
If 63.8 PSI feels high for your conditions, step up one ISO size (e.g., from 04 Red to 05 Brown) to bring pressure down toward mid-band.

ISO Nozzle Size and Color (rated flow @ 40 PSI)

• 01 – Orange – 0.10 GPM
• 015 – Green – 0.15 GPM
• 02 – Yellow – 0.20 GPM
• 025 – Purple – 0.25 GPM
• 03 – Blue – 0.30 GPM
• 04 – Red – 0.40 GPM
• 05 – Brown – 0.50 GPM
• 06 – Gray – 0.60 GPM
• 08 – White – 0.80 GPM
• 10 – Light Blue – 1.00 GPM
• 12 – Light Green – 1.20 GPM

Pro Tips for Accurate Applications

• Measure true ground speed in the field; console readings can be off.
• Replace worn nozzles—5–10% extra flow from wear is common after heavy use.
• Spray with proper boom height that will maintain adequate overlap for the spray angle of your nozzles.
• Re-check pressure and droplet size required to stay “on label” whenever you change rate, speed, or product.

Related Guides on Sprayer Guru

• What Do the Numbers on a Sprayer Nozzle Mean?
• Guide to Spray Nozzle Charts
• Spray Nozzle Color Code

FAQ: Nozzle Pressure and Target GPA

Q: How do I calculate nozzle pressure for a target GPA?
A: Use the calculator. It converts your rate, speed, and spacing into per-nozzle flow, then applies P₂ = P₁ × (Q₂ / Q₁)² using your nozzle’s rating.

Q: What PSI should I spray at?
A: It depends on the nozzle family and your target droplet class. Many flat-fans operate in the ~20–60 PSI range; confirm on your nozzle chart and verify droplet class.

Q: How do speed and spacing affect GPA?
A: Faster speed or wider spacing increases the flow each nozzle must deliver, which pushes the required pressure higher.

Q: What if my required PSI is outside my comfort range?
A: Swap nozzle size. Go smaller to raise PSI or larger to lower PSI, aiming for your preferred mid-band.

Q: Do I need to change nozzles for different products?
A: Often, yes. Labels specify droplet class and coverage goals. Re-run the calculator when rates or speeds change, and confirm droplet class on the chart.