PSI to GPM Calculator - Convert Pressure to Flow Rate
Free PSI to GPM calculator for determining water flow rate in gallons per minute (GPM) from pressure difference (PSI) and pipe dimensions. Our calculator uses Bernoulli's equation for incompressible fluids to provide accurate flow rate calculations. Perfect for hydraulic systems, plumbing design, irrigation systems, and fluid dynamics applications.
Last updated: January 24, 2026
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Default: 14.7 psi (atmospheric pressure)
Enter either diameter or cross-sectional area
How it works:
Enter the pressure inside the tank and at the exit, then provide either the pipe diameter or cross-sectional area. The calculator uses Bernoulli's equation to determine the flow rate.
Understanding PSI and GPM
Definition
1 PSI = 1 lbf/in²
PSI measures pressure - the force applied per unit area. It's commonly used in the United States for measuring pressure in various applications.
- Used for tire pressure measurements
- Common in hydraulic systems
- Standard for water pressure in plumbing
Definition
Volume flow rate
GPM measures flow rate - how fast liquid moves through a pipe or system. It's essential for sizing pumps, pipes, and hydraulic components.
- Used in plumbing and irrigation
- Critical for pump sizing
- Important for system design
Quick Example Result
For a tank with 72 PSI pressure, 14.7 PSI exit pressure, and 2.5 inch pipe diameter:
Pressure Difference
57.3 PSI
Flow Rate
~1,412 GPM
Pipe Diameter
2.5 inches
How Our PSI to GPM Calculator Works
Our PSI to GPM calculator uses Bernoulli's equation for incompressible fluids to determine flow rate from pressure difference and pipe dimensions. The calculation accounts for pressure differences, fluid density, and pipe cross-sectional area to provide accurate flow rate estimates for water systems.
Bernoulli's Equation
P₁ + ½ρv₁² = P₂ + ½ρv₂²For horizontal flow: P₁ - P₂ = ½ρ(v₂² - v₁²)Velocity: v = √[2(P₁ - P₂) / ρ]Flow Rate: Q = v × AWhere P is pressure, ρ is fluid density, v is velocity, and A is cross-sectional area. For water at standard conditions, density is 62.4 lb/ft³. The calculator assumes the tank velocity (v₁) is negligible compared to the pipe velocity.
Calculation Steps
The calculator performs the following steps to convert PSI to GPM:
- Calculate pressure difference: Subtract exit pressure from tank pressure (PSI)
- Convert to consistent units: Convert PSI to pound-force per square foot (lbf/ft²)
- Apply Bernoulli's equation: Calculate flow velocity from pressure difference and water density
- Determine pipe area: Calculate cross-sectional area from diameter (or use provided area)
- Calculate flow rate: Multiply velocity by cross-sectional area to get volume flow rate
- Convert to GPM: Convert cubic feet per second to gallons per minute
Practical Applications
PSI to GPM calculations are essential in many engineering and practical applications. Hydraulic system designers need to know flow rates to size pumps and pipes correctly. Plumbers use these calculations to ensure adequate water pressure and flow. Irrigation engineers calculate flow rates to design efficient watering systems.
Common Use Cases:
- • Hydraulic systems: Calculating flow rates for hydraulic machinery and equipment
- • Plumbing design: Determining pipe sizes and pump requirements for water distribution
- • Irrigation systems: Sizing pipes and calculating flow rates for agricultural irrigation
- • Fire suppression: Calculating water flow rates for sprinkler systems and fire hydrants
- • Industrial processes: Designing fluid transport systems in manufacturing
- • Pump selection: Determining required pump capacity based on pressure and flow needs
Important Considerations
The calculator uses ideal fluid dynamics assumptions (Bernoulli's equation for frictionless, incompressible flow). In real-world applications, factors like pipe friction, fittings, valves, and fluid viscosity will reduce actual flow rates. The calculated values represent theoretical maximum flow rates under ideal conditions.
Sources & References
- Fluid Mechanics: Fundamentals and Applications - Yunus A. Çengel, John M. CimbalaComprehensive reference for Bernoulli's equation and fluid flow calculations
- Hydraulic Engineering - Bruce E. Larock, Roland W. Jeppson, Gary Z. WattersPractical applications of flow rate calculations in hydraulic systems
- Khan Academy - Bernoulli's Equation and Fluid FlowEducational resources for understanding fluid dynamics principles
Need help with other conversions? Check out our pressure converter and volume conversion.
Get Custom Calculator for Your PlatformPSI to GPM Calculator Examples
Input:
- Pressure inside tank: 72.0 PSI
- Pressure at exit: 14.7 PSI
- Pipe diameter: 2.5 inches
- Water density: 62.4 lb/ft³
Calculation Steps:
- Step 1: Pressure difference: 72.0 - 14.7 = 57.3 PSI
- Step 2: Convert to lbf/ft²: 57.3 × 144 = 8,251.2 lbf/ft²
- Step 3: Calculate velocity: v = √[2(P₁-P₂)/ρ] = 92.24 ft/s
- Step 4: Calculate area: A = π(1.25/12)² = 0.0341 ft²
- Step 5: Flow rate: Q = v × A = 3.145 ft³/s
- Step 6: Convert to GPM: 3.145 × 448.83 = 1,412 GPM
Result: Flow rate is approximately 1,412 gallons per minute (GPM)
This calculation assumes ideal conditions with no friction losses. Actual flow rates may be lower due to pipe friction, fittings, and other real-world factors.
Lower Pressure Example
30 PSI tank, 14.7 PSI exit, 1 inch pipe
Flow rate ≈ 113 GPM
Larger Pipe Example
50 PSI tank, 14.7 PSI exit, 4 inch pipe
Flow rate ≈ 1,808 GPM
Frequently Asked Questions
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