How to use this tool
- Enter pipe inside diameter, length and volumetric flow rate.
- Enter fluid density, dynamic viscosity and wall roughness.
- Optionally add minor-loss coefficient, elevation gain and pump efficiency.
- Check Reynolds regime, calculated friction and estimated head/power before selecting real equipment.
Calculation method and formula
Re = ρ v D/μ. Darcy pressure loss Δp = [f (L/D) + ΣK] ρv²/2. For laminar flow f = 64/Re; turbulent friction uses the Swamee–Jain approximation.
WORKED EXAMPLE
A smooth 10 mm inside-diameter pipe, 1.25 m long, carrying fluid at 0.1 m/s with density 1,000 kg/m³ and dynamic viscosity 0.001 Pa·s gives Re = 1,000 and friction pressure loss = 40 Pa.
What the calculation does not cover
- This assumes incompressible, steady, fully developed single-phase flow.
- The transitional regime (Re 2,300–4,000) is deliberately rejected due to friction uncertainty.
- Pump selection requires a system curve, NPSH, cavitation review and manufacturer pump curve.
Common questions
Why won't it calculate Re = 3,000?
It is within the transitional range, where neither the laminar nor standard turbulent expression is reliably applicable.
Does estimated shaft power select a pump?
No. It is a power estimate and cannot replace a supplier's pump curve and NPSH analysis.
Engineering use: This calculator is a transparent estimate for its defined model; confirm units, applicability, standards and engineering decisions independently.