Pipe Flow Calculator
Calculate pressure drop, flow velocity, Reynolds number, and friction factor using the Darcy-Weisbach equation with Swamee-Jain approximation.
Pipe & Fluid Parameters
ΔP = f × (L/D) × (ρv²/2) | Swamee-Jain: f = 0.25/[log(ε/3.7D + 5.74/Re0.9)]²
Pressure Drop
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Velocity (ft/s)
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Reynolds Number
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Flow Regime
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Additional Details
Friction Factor
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Velocity Head (ft)
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ΔP per 100 ft
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Head Loss (ft)
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Pressure Drop vs. Flow Rate
How this was calculated
Darcy-Weisbach: dP = f * (L/D) * (rho*v^2/2). Converted to psi from lb/ft^2 by dividing by 144.
Reynolds number: Re = rho*v*D/mu. If Re < 2300 = laminar, 2300-4000 = transitional, > 4000 = turbulent.
Friction factor: Laminar: f = 64/Re. Turbulent: Swamee-Jain explicit approximation of Colebrook-White.
Roughness: Default 0.0018 in for commercial steel. PVC ~0.00006 in, cast iron ~0.01 in.
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Book a free strategy call →Understanding Pipe Flow and Pressure Drop
The Darcy-Weisbach equation is the fundamental relationship for calculating frictional pressure loss in pipes. It applies to all Newtonian fluids and flow regimes. The friction factor depends on the Reynolds number and relative pipe roughness: in laminar flow (Re < 2300), f = 64/Re regardless of roughness; in turbulent flow, the Colebrook-White equation (or its explicit Swamee-Jain approximation) is used. Proper pressure drop estimation is critical for pump sizing, pipeline design, and production system optimization.
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