Pipe Flow Velocity Calculator
Convert volumetric flow rate (what your pump delivers) into the average flow velocity inside a pipe. Velocity is the key input for calculating Reynolds number and ultimately the friction factor and pressure drop in any pipe system.
Calculate Flow Velocity from Flow Rate
Results
Why Velocity Matters in Pipe Flow
Flow rate tells you how much fluid moves through a pipe - useful for process design and pump selection. But velocity tells you how fast that fluid moves - which controls friction losses, pipe erosion, noise, and the all-important Reynolds number.
In practice, engineers often work backwards: start with a required flow rate (from the process), choose a pipe size, calculate velocity, then check Reynolds number and friction factor to confirm the design is acceptable. This calculator handles the first step.
The Formula Explained
V = Q / A = 4Q / (π × D²) - V - average flow velocity (m/s)
- Q - volumetric flow rate (m³/s)
- A - pipe cross-sectional area = π × D² / 4 (m²)
- D - pipe internal diameter (m)
Note this gives the average velocity across the pipe cross-section. In reality, velocity is zero at the pipe wall and highest at the center (with a parabolic profile in laminar flow, flatter in turbulent flow). The average is what matters for flow calculations.
Typical Design Velocities
Worked Example
A pump delivers 28.3 m³/h through a 100 mm (0.1 m) diameter pipe. What is the flow velocity?
Q = 28.3 / 3600 = 0.00786 m³/s
A = π × (0.1)² / 4 = 0.007854 m²
V = 0.00786 / 0.007854
V ≈ 1.00 m/s
With V = 1.0 m/s and D = 0.1 m, you can now calculate Re using our Reynolds Number Calculator (you'll also need kinematic viscosity).
Frequently Asked Questions
What's the difference between velocity and flow rate?
Flow rate (Q) is the volume of fluid passing a point per second - it depends on both velocity and pipe size. Velocity (V) is how fast the fluid moves. A small pipe at high velocity can carry the same flow rate as a large pipe at low velocity: Q = V × A.
How do I convert L/min to m³/s?
Divide by 60,000. For example, 100 L/min = 100 / 60,000 = 0.001667 m³/s. Or: multiply by 0.00001667.
Does velocity change along the pipe length?
For incompressible fluids (liquids) in a constant-diameter pipe, velocity stays constant along the pipe. It only changes when the diameter changes (pipes narrowing or widening). For compressible fluids (gases), density changes can affect velocity too.
Related Tools
🌊 Reynolds Number Calculator
Use velocity from this tool to calculate Reynolds number - the next step.
🔄 Volumetric Flow Rate Calculator
Reverse this calculation - find flow rate from velocity and diameter.
📊 Moody Chart Calculator
After finding Re, use the Moody Chart to get friction factor.
📉 Pressure Drop Calculator
Use velocity to calculate pressure loss in your pipe system.