About the Fluid Velocity Calculator
Fluid velocity in a pipe from flow rate and diameter, with the continuity equation for size changes.
Also known as: pipe velocity, water velocity, continuity equation.
How to use this calculator
- Enter flow rate, pipe inside diameter, second pipe diameter (optional).
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
v = Q / A · A₁v₁ = A₂v₂
Worked example
Using the values pre-filled in the calculator above:
- Flow rate = 100 L/min
- Pipe inside diameter = 50 mm
- Second pipe diameter (optional) = 25 mm
the calculator returns:
- Velocity: 0.849 m/s
- Pipe area: 1,963.5 mm²
- Velocity (ft/s): 2.78
- Velocity in 25 mm pipe: 3.395 m/s