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Piping

Pipe Velocity / Flow / Diameter Calculator

This calculator solves the continuity equation for incompressible flow in a circular pipe, computing any one of average velocity, volumetric flow rate or internal diameter from the other two using Q = v × πD²/4.

Flow through a circular pipe relates velocity, volumetric flow rate, and pipe cross-sectional area. Given any two of velocity, flow, and internal diameter, this calculator solves for the third using the continuity equation for incompressible flow.

TypeInteractive engineering calculator

Calculator

Result
Velocity0.63662 m/s

Formulas

Cross-sectional area
A = πD² / 4
Velocity from flow
v = Q / A
Flow from velocity
Q = v × A
Diameter from flow and velocity
D = √(4Q / (πv))

Diagram

Pipe Cross-Section: Internal Diameter and VelocityD (internal)vv = Q / AA = πD²/4

Worked example

Water flows at 0.005 m³/s through a pipe with internal diameter 100 mm. What is the velocity?

  1. 01Convert diameter: 100 mm = 0.1 m
  2. 02A = π × 0.1² / 4 = 0.007854 m²
  3. 03v = Q / A = 0.005 / 0.007854
  4. 04v ≈ 0.6366 m/s
Result

The average pipe velocity is approximately 0.637 m/s.

FAQ

Does this include pipe schedule lookup?
No. You must enter the actual internal diameter. Pipe schedule lookup is not implemented.
Does this calculate pressure drop?
No. Pressure drop calculation requires friction factor, pipe length, and fittings data, which are outside the scope of this calculator.
Does this calculate Reynolds number?
No. Reynolds number calculation is deferred to a future release.
Is this velocity the centreline velocity?
No. This is the average (bulk) velocity across the pipe cross-section, which is what is used for most engineering calculations.

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