Pipe Flow Pressure Drop Calculator | Darcy-Weisbach

Pipe & Fluid Parameters

Pipe Diameter (mm)

Pipe Length (m)

Flow Rate (m³/hr)

Roughness ε (mm)

Flow Analysis

Turbulent Flow

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Pressure Drop ΔP
0
kPa

Head Loss h_f

Flow Velocity

m/s

Reynolds Number Re

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Darcy Friction Factor f

Relative Roughness

Energy Loss

📐 Darcy-Weisbach Equation: h_f = f × (L/D) × (v²/2g) • ΔP = ρ × g × h_f
Friction factor f from Colebrook equation (iterative solution) • Reynolds number determines laminar/turbulent flow regime

The Darcy-Weisbach equation is the industry standard for calculating pressure drop due to friction in pipe flow. This calculator solves the Colebrook equation iteratively for the friction factor, providing accurate results for both laminar and turbulent flow.

Use this tool to size pumps, select pipe diameters, and optimize fluid transport systems.

— Vaibhav Dhokpande, Developer · TaskJunction

📖 Pipe Flow & Pressure Drop — Practical Guide

Pressure drop in a pipe is calculated using the Darcy-Weisbach equation: ΔP = f × (L/D) × (ρV²/2). The friction factor (f) depends on whether the flow is laminar or turbulent — determined by the Reynolds number: Re = ρVD/μ.

For laminar flow (Re < 2300), f = 64/Re. For turbulent flow (Re > 4000), the Moody chart or Colebrook-White equation is used. In practice, most industrial pipe flows are turbulent.

The minor losses (bends, valves, fittings) are often significant — sometimes exceeding the pipe friction loss in short systems. These are calculated using the equivalent length method or K-factor method.

Typical Flow Velocities

Fluid	Recommended Velocity	Reason
Water (supply)	0.5–2.0 m/s	Erosion, noise
Water (return)	0.3–1.5 m/s	Sedimentation
Compressed Air	6–10 m/s	Pressure drop
Hydraulic Oil	2–4 m/s (pressure lines)	Heat, erosion

Design rule: Keep pressure drop across the distribution system below 10% of the available supply pressure. Higher than that and your pumps are working harder than necessary — energy waste and increased operating cost.