Reynolds number and line velocity
Velocity, Reynolds number, flow regime, friction factor and pressure gradient for any liquid in any pipe — water properties built in.
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How this calculator works
Velocity v = Q / A, Reynolds number Re = ρvD/μ. The flow is laminar below Re ≈ 2,000, turbulent above ≈ 4,000 and transitional in between. The Darcy friction factor comes from the Colebrook equation (64/Re when laminar), and the friction gradient from Darcy–Weisbach, ΔP/L = f·ρv²/(2D). Water density and viscosity come from IAPWS-IF97 and IAPWS 2008 for the temperature you enter.
Example: 100 m³/h of water at 20 °C in 4-inch Schedule 40 steel pipe (102.26 mm ID): velocity 3.38 m/s, Re = 344,700 (turbulent), f = 0.0177, and about 0.99 bar of friction loss per 100 m — fast for a liquid line, so the next size up (6 inch, 1.49 m/s) would normally be chosen.
Velocity guides are common design practice for liquid lines (about 1–3 m/s; pump suctions slower); use your own company line-sizing criteria. References: Perry's Chemical Engineers' Handbook §6; Crane, Flow of Fluids (TP-410); Colebrook (1939).