Pipe Flow Rate & Velocity Calculator
Calculate fluid velocity based on pipe diameter and flow rate.
Inches (in)
Millimeters (mm)
US Gallons Per Minute (GPM)
Cubic Meters Per Hour (m³/h)
Liters Per Second (L/s)
Calculation Results
Velocity (Feet/sec)
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Velocity (Meters/sec)
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Understanding Pipe Flow Velocity
Fluid velocity is a critical measurement in hydraulic and piping design. It represents how fast a liquid or gas moves through a cross-section of a pipe. Maintaining the correct velocity is essential for preventing pipe erosion, minimizing pressure drops, and ensuring solids do not settle in the line.
The Physics of Flow
The calculation is based on the Principle of Continuity. For an incompressible fluid, the flow rate (Q) is equal to the cross-sectional area (A) multiplied by the velocity (v). Mathematically, this is expressed as:
Velocity (v) = Flow Rate (Q) / Area (A)
Standard Design Recommendations
- Water Supply: Typically 3 to 7 feet per second (0.9 to 2.1 m/s).
- Suction Lines: Usually lower, around 2 to 4 fps (0.6 to 1.2 m/s) to prevent cavitation.
- Drain Lines: Minimum of 2 fps (0.6 m/s) to ensure "self-cleansing" velocity.
- Erosion Risk: Velocities exceeding 10-12 fps (3-3.6 m/s) can lead to rapid pipe wear and noise.
Practical Example
Imagine you have a 2-inch Schedule 40 pipe (actual inner diameter of 2.067 inches) and a flow rate of 50 GPM.
- Convert diameter to area: A = π × (r²) ≈ 3.35 square inches.
- Apply the velocity conversion: v = (50 GPM × 0.4085) / (2.067²) ≈ 4.78 ft/s.
- This result falls within the ideal range for general water distribution.