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🔧 Pipe Sizing Calculator

Pipe Sizing Calculator

Inputs

Results

Recommended Diameter- in
Actual Velocity- ft/s
Reynolds Number-
Flow Regime-

Calculator Description

Pipe sizing determines the optimal pipe diameter based on flow rate and allowable velocity. Excessive velocity increases frictional pressure drop, while too low velocity raises equipment costs.

What this calculator finds

Enter the flow rate and allowable velocity to calculate the minimum pipe diameter, and the closest standard pipe specification (KS, ANSI, JIS, etc.) is recommended. Velocity, friction factor, and pressure drop are also calculated.

Why it matters

  • Piping costs (pipe+fittings+installation) account for 30–50% of total plant cost, making economical sizing important
  • Excessive velocity causes erosion, vibration, and noise
  • Pipe size determines pump power and operating costs

Formula

Pipe Sizing Formulas

The basic principle is the continuity equation (flow conservation) and the velocity–cross-section relationship.

Q=AvQ = A v
A=πD24A = \dfrac{\pi D^{2}}{4}
D=4QπvD = \sqrt{\dfrac{4Q}{\pi v}}
  • Q — Volumetric flow rate [m³/s]
  • A — Pipe cross-sectional area [m²]
  • v — Velocity [m/s]
  • D — Pipe inner diameter [m]

Frictional Pressure Drop (Darcy-Weisbach)

ΔP=f LD ρv22\Delta P = f\,\dfrac{L}{D}\,\dfrac{\rho v^{2}}{2}
  • ΔP — Frictional pressure drop [Pa]
  • f — Darcy friction factor (dimensionless)
  • L — Pipe length [m]
  • ρ — Fluid density [kg/m³]

Recommended velocity ranges

  • Water supply piping: 1.0–2.0 m/s
  • Hot water piping: 0.8–1.5 m/s
  • Steam piping: 20–40 m/s (saturated steam)
  • Chilled water piping: 1.0–2.5 m/s

Useful Tips

Practical tips

  • It is common to select one standard size larger than the theoretical minimum diameter
  • Shorter, larger-diameter pipes have less friction loss, so larger diameters are preferred within the economic velocity range
  • High-viscosity liquids (oil, etc.) require lower design velocities

Limitations & cautions

  • This calculator is for steady-state flow; water hammer and transient flow require separate analysis
  • Minor losses from fittings and bends are not included and require separate equivalent length conversion
  • Design diameter should have margin to account for corrosion and scale buildup