Pipe Size & Water Velocity Calculator
Calculate pipe inner diameter, water velocity, or volumetric flow rate using the continuity equation Q = A × V for circular pipes.
Formulas Used
Continuity Equation:
Q = A × V
where A = (π / 4) × D²
Therefore:
- Velocity: V = Q / A = 4Q / (π × D²)
- Diameter: D = √(4Q / (π × V))
- Flow Rate: Q = (π / 4) × D² × V
Reynolds Number: Re = (V × D) / ν
where ν = 1.004 × 10⁻⁶ m²/s (kinematic viscosity of water at 20°C)
Assumptions & References
- Pipe cross-section is circular and uniform along its length.
- Flow is steady-state and incompressible (water density ≈ 998 kg/m³ at 20°C).
- Diameter entered is the inner (bore) diameter, not the outer diameter.
- Kinematic viscosity of water assumed at 20°C (ν = 1.004 × 10⁻⁶ m²/s) for Reynolds number calculation.
- Recommended velocity range for water distribution: 0.3 – 3.0 m/s (AWWA, CIBSE Guide G).
- Flow regimes: Laminar (Re < 2300), Transitional (2300 ≤ Re < 4000), Turbulent (Re ≥ 4000).
- References: White, F.M. — Fluid Mechanics, 8th Ed.; AWWA M11 Steel Pipe Design Manual; CIBSE Guide C.