Determine the exact flow rate or operating pressure for any spray nozzle. Enter your nozzle's catalog values and instantly calculate performance using the industry-standard square root pressure-flow relationship.
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How to Calculate Spray Nozzle Flow Rate
Every spray nozzle follows a fundamental hydraulic principle: flow rate is proportional to the square root of pressure. This means small pressure changes produce predictable shifts in flow, and this calculator leverages that relationship to give you precise results.
The Pressure–Flow Formula
To find the required pressure for a target flow rate:
P₂ = P₁ × (Q₂ ÷ Q₁)²
P = pressure | Q = flow rate | 1 = known | 2 = target
To find the resulting flow rate at a new pressure:
Q₂ = Q₁ × √(P₂ ÷ P₁)
Enter your catalog values for P₁ and Q₁, then the new pressure P₂
Key Concepts
Square root relationship: Doubling pressure increases flow by ~41%. To double flow, you need 4× the pressure.
Specific gravity (SG): Water has an SG of 1.0. Heavier fluids (oils, chemicals) require adjusted calculations. Enter your fluid's SG for accurate results.
Nozzle type matters: While the pressure-flow math is universal, different nozzle geometries (flat fan, full cone, hollow cone) have different discharge coefficients. Select your nozzle type for best accuracy.
Catalog reference values: Use the pressure and flow values from your nozzle's data sheet as the "current" or "reference" inputs for the most reliable calculations.
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Use the formula Q₂ = Q₁ × √(P₂ ÷ P₁), where Q₁ is the known flow rate at reference pressure P₁, and P₂ is your new operating pressure. Enter your nozzle's catalog pressure and flow rate into the calculator above, then input the new pressure to instantly see the resulting flow rate in GPM or LPM.
To find the required pressure for a target flow rate, use P₂ = P₁ × (Q₂ ÷ Q₁)². For example, if your nozzle flows 2.0 GPM at 40 PSI and you need 3.0 GPM, the required pressure is 40 × (3.0 ÷ 2.0)² = 90 PSI. This calculator handles the math automatically.
Flow rate is proportional to the square root of pressure. This means doubling the pressure increases flow by approximately 41% — not double. To achieve double the flow rate, you need to increase the pressure by a factor of four. This square root relationship applies to all hydraulic spray nozzles regardless of type.
Specific gravity (SG) is the density of your fluid relative to water (SG = 1.0). Adjust this value when spraying fluids other than water — for example, light oils (SG ≈ 0.8–0.9), chemical solutions (SG ≈ 1.0–1.4), or slurries (SG > 1.0). Heavier fluids require more pressure to achieve the same flow rate as water.
The calculator supports both U.S. customary units (PSI for pressure, GPM for flow rate) and metric units (bar for pressure, LPM for flow rate). Use the toggle at the top of the calculator to switch between systems. All formulas and results update automatically.
The fundamental pressure-flow relationship (square root law) applies to all nozzle types. However, different nozzle geometries — flat fan, full cone, hollow cone, solid stream, and spiral — have different internal flow characteristics. Selecting the correct nozzle type helps ensure the most accurate result for your specific application.
