Pipe Flow Rate Calculator
Determine volumetric flow rate based on pipe diameter and velocity.
mm
cm
meters
inches
m/s
ft/s
Please enter valid positive numbers for diameter and velocity.
Calculation Results
Cubic Meters per Hour:
0 m³/h
Liters per Minute:
0 L/min
US Gallons per Minute:
0 GPM
Liters per Second:
0 L/s
Cross-Sectional Area:
0 mm²
Understanding Pipe Flow Rate
Calculating the flow rate of fluid through a pipe is a fundamental task in hydraulic engineering, plumbing, and irrigation system design. The volumetric flow rate determines how much fluid passes through a specific cross-section of a pipe within a given time frame.
The Flow Rate Formula
The calculation uses the continuity equation for incompressible fluids. The basic formula is:
Q = A × v
Where:
- Q = Volumetric Flow Rate
- A = Cross-sectional Area of the pipe
- v = Average Velocity of the fluid
How to Calculate Area
Since pipes are generally circular, the cross-sectional area is calculated using the pipe's inner diameter:
A = π × (Diameter / 2)² or A = (π × Diameter²) / 4
Why Inner Diameter Matters
When measuring your pipe, it is critical to use the Inner Diameter (ID), not the outer diameter. The wall thickness of the pipe does not carry fluid. For standard pipes (like Schedule 40 PVC), the inner diameter differs significantly from the nominal pipe size.
Common Flow Rate Units
- m³/h (Cubic meters per hour): Commonly used in industrial pump specifications and large water treatment plants.
- L/min (Liters per minute): Standard for household plumbing fixtures and showers.
- GPM (Gallons per minute): The standard unit in the United States for pumps, irrigation, and plumbing.
- ft/s or m/s: These measure velocity, not volume, but are crucial for preventing water hammer or pipe erosion.
Typical Flow Velocities
Design engineers often aim for specific velocity ranges to maintain efficiency:
- Water Supply: 0.9 to 2.4 m/s (3 to 8 ft/s)
- Drainage: High enough to be self-cleaning, but low enough to prevent noise.
- Suction Lines: Lower velocities are preferred to prevent cavitation.