Pipe Flow Rate & Pressure Drop Calculator
Enter pipe material, diameter, flow rate, and length to instantly get velocity, flow regime, and Darcy-Weisbach pressure drop. Add multiple pipe runs for a full system schedule. Nothing uploaded.
Results
System run schedule
| Dia | Flow | Length | Velocity | dP |
|---|
Learn more: pipe flow and pressure drop calculations
Darcy-Weisbach equation and friction factor for different pipe materials
Pressure drop in flowing liquid depends on fluid velocity, pipe diameter, pipe length, and friction factor - which varies by pipe material and flow regime. Smooth pipes (copper, PVC) have lower friction than rough pipes (galvanized steel, concrete). The calculator uses Darcy-Weisbach equation: DP = f × (L/D) × (ρV²/2), where f is friction factor, L is length, D is diameter, ρ is density, V is velocity.
Laminar vs turbulent flow and Reynolds number
In laminar flow (Re < 2300), friction factor depends only on viscosity. In turbulent flow (Re > 4000), friction increases with pipe roughness. The transition determines which friction factor equation applies. The calculator checks Reynolds number and applies correct friction model for your flow conditions.
How to estimate pressure loss in your piping system
Measure pipe diameter, total length (including elbows and fittings), fluid velocity or flow rate, and fluid type. The calculator outputs pressure drop in psi, bar, or pascals. Use this to size your pump - the pump must deliver enough pressure to overcome system friction plus any static height difference.
FAQ
Why does pressure drop matter?
High pressure drop means your pump must work harder to move fluid through the system, wasting energy and increasing costs. Proper sizing prevents undersized pipes that cause excessive pressure loss.
What causes high pressure drop?
Small pipe diameter, high flow rate, rough pipe interior, and long pipe runs all increase pressure drop. Using a larger diameter pipe dramatically reduces it.
Should I account for fittings and elbows?
Yes. Each elbow, valve, and fitting adds equivalent length to your system. A 90-degree elbow is often equivalent to 20-30 pipe diameters of straight pipe.