Enter flow rate and pipe parameters to calculate velocity, Reynolds number, flow regime and pressure drop using the Darcy-Weisbach equation with Colebrook-White friction factor. ASME B36.10 built-in with custom schedule option.
Darcy-Weisbach equation. Friction factor by iterative Colebrook-White solution (50 iterations). Pipe data per ASME B36.10M.
Calculating pressure drop and flow velocity in a pipe is one of the most frequent tasks in process piping design. Engineers use these results to verify that pipe velocities are within acceptable limits, that pressure drop is within the available driving force, and that the selected pipe size gives a cost-effective design. This tool uses the Darcy-Weisbach equation with the Colebrook-White friction factor — the most accurate and universally applicable method for pipe flow calculation.
The result includes flow velocity, Reynolds number, flow regime, Darcy friction factor, pressure drop in bar, psi and metres of water column, and pressure drop per 100 metres — the most practical unit for comparing pipe sizes during line sizing.
Unlike the Hazen-Williams equation which is limited to water at ambient conditions, Darcy-Weisbach applies to any Newtonian fluid at any temperature — making it correct for hydrocarbons, chemicals, steam condensate and all process fluids. The friction factor is solved iteratively using Colebrook-White, which gives accurate results across laminar flow (Re below 2300), transitional and fully turbulent flow (Re above 4000).
Velocities below the minimum cause sedimentation in liquid lines and poor flow distribution. Velocities above the maximum cause erosion at fittings, flow-induced vibration, noise, and disproportionately high pressure drop.
New carbon steel: 0.046 mm. Corroded carbon steel in service: 0.15 to 0.30 mm. Stainless steel: 0.015 mm. PVC or smooth plastic: 0.0015 mm. Roughness significantly affects pressure drop in fully turbulent flow at high Reynolds numbers.
No — this calculates straight pipe friction loss only. For a complete line hydraulic calculation, add the equivalent length of all fittings (elbows, tees, valves, reducers) to the straight pipe length, or calculate fitting losses using the K-value or 2K method and add them separately.
Reynolds number characterises the flow regime. Re below 2300: laminar flow (f = 64/Re, smooth parabolic velocity profile). Re 2300 to 4000: transitional (unstable, avoid if possible). Re above 4000: turbulent flow (Colebrook-White applies, flat velocity profile). Most process piping operates in turbulent flow.
Pressure drop calculation uses the Darcy-Weisbach equation with Colebrook-White friction factor. Pipe inside diameters per ASME B36.10M. Roughness values per ASME B46.1. This tool calculates straight pipe friction loss for preliminary line sizing. Final hydraulic calculations should be verified with a validated process simulation tool such as HYSYS, PRO/II or PIPESIM.