Pipe Flow Calculator
Calculate flow velocity, Reynolds number, and pressure drop for liquid flow through a straight pipe run.
Enter your values
Flow rate, pipe geometry, and fluid properties.
How this calculator works
Flow velocity comes directly from continuity — flow rate divided by pipe cross-sectional area:
Reynolds number determines the flow regime:
For laminar flow (Re < 2300), the Darcy friction factor is f = 64/Re. For turbulent flow (Re > 4000), the calculator uses the Swamee-Jain approximation to the Colebrook equation. Pressure drop then follows from Darcy-Weisbach:
Flow regime reference
| Reynolds number | Regime |
|---|---|
| < 2,300 | Laminar |
| 2,300 – 4,000 | Transitional |
| > 4,000 | Turbulent |
Frequently asked questions
What roughness value should I use?
Commercial steel pipe is commonly taken as 0.045 mm, PVC/plastic pipe around 0.0015 mm, and drawn copper or glass as effectively smooth. Use the manufacturer's value where available.
Does this include fittings and valves?
No — this covers straight-pipe friction loss only. Fittings, valves, and bends add additional minor losses that should be summed separately using their loss coefficients (K values).