Enter density, velocity, diameter and viscosity — get Re, the flow regime and the friction factor.
Open the free calculator →The Reynolds number tells you whether pipe flow is laminar or turbulent — which sets the friction factor, heat-transfer correlation and mixing behaviour you should use. EnggiBasis computes Re, classifies the regime, and returns the Darcy friction factor in one go.
Re = ρ · v · D / μ
where ρ = density, v = velocity, D = internal diameter, μ = dynamic viscosity. Re is dimensionless — it's the ratio of inertial to viscous forces.
| Reynolds number | Regime |
|---|---|
| Re < 2300 | Laminar |
| 2300 – 4000 | Transitional |
| Re > 4000 | Turbulent |
EnggiBasis returns the Darcy friction factor: f = 64/Re in laminar flow, or the Colebrook-White equation (a function of Re and relative roughness) in turbulent flow.
| Input | Value |
|---|---|
| Density | 1000 kg/m³ |
| Velocity | 2 m/s |
| Diameter | 100 mm |
| Viscosity | 1 cP |
Result: Re = 1000 × 2 × 0.1 / 0.001 = 200,000 → turbulent, friction factor ≈ 0.0186. Try your own numbers →
Re = ρvD/μ in consistent units → a dimensionless number.
Pipe flow: laminar below ~2300, transitional 2300–4000, turbulent above 4000.
Yes — free, with regime and friction factor included.
Related: Line sizing · Tank volume · Unit converter