Fast pipe-loss insight for engineers and students. Enter flow details or Reynolds number and roughness. Haaland method delivers friction factor plus export-ready summaries today.
This calculator returns the Darcy friction factor used in the Darcy–Weisbach equation.
For transitional flow, results are approximate and should be validated.
| Mode | Re | ε/D | Estimated f | Typical regime |
|---|---|---|---|---|
| Direct | 100000 | 0.00020 | ≈ 0.0186 | Turbulent |
| Direct | 1500 | 0.00000 | ≈ 0.0427 | Laminar |
| Flow | ≈ 99800 | ≈ 0.00090 | ≈ 0.0221 | Turbulent |
Values are illustrative; your results depend on inputs and units.
Pressure loss in straight pipe is commonly estimated with the Darcy–Weisbach relation. The friction factor controls how strongly velocity and length increase head loss. Small changes in f can shift pump power, valve sizing, and operating cost.
Reynolds number compares inertial forces to viscous forces. For internal flow, laminar behavior is often expected below about 2000, while fully turbulent flow is commonly assumed above about 4000. Transitional cases require engineering judgment and sensitivity checks.
Relative roughness, ε/D, represents wall texture compared with diameter. New smooth tubing can have very small ε/D, while older or scaled systems may increase ε/D significantly. When ε/D rises, the friction factor trends upward, especially at high Reynolds number.
The Haaland relation is an explicit approximation to the implicit Colebrook formulation. It avoids iterative solving and is fast for repeated calculations. It performs well for turbulent flow across wide ranges of Reynolds number and roughness used in engineering practice.
For many water and air systems, friction factors often fall between about 0.008 and 0.08. Smooth, high-Re flows can approach the lower end. Rough, moderate-Re flows can move higher. Always validate against expected material roughness and measured pipe diameter.
When you enter diameter, velocity, density, and viscosity, the calculator computes Re = ρVD/μ. This helps when you have process conditions rather than a precomputed Reynolds number. Keep property values consistent with temperature and fluid composition for reliable results.
Once f is known, you can estimate straight-pipe losses using ΔP = f(L/D)(ρV²/2). Combine this with minor losses from fittings and valves for a complete model. If the system is long, check how changing flow alters Re and therefore friction factor.
This calculator returns the Darcy friction factor used in the Darcy–Weisbach equation. If you need the Fanning factor, it is typically one quarter of the Darcy value for the same conditions.
It is best suited for turbulent flow, generally when Re is above about 4000. It is also useful for rapid design iterations because it avoids iterative solving.
The calculator switches to the laminar correlation f = 64/Re. In laminar flow, friction factor depends strongly on viscosity and Reynolds number, not on wall roughness.
Start with typical published roughness values for your pipe material and age. If deposits or corrosion are likely, consider using conservative higher roughness, then refine with inspection or measured pressure drop.
No. This tool computes the straight-pipe friction factor only. For a full system model, add minor losses using K values or equivalent length methods, then combine them with Darcy–Weisbach straight-pipe losses.
They should not, if inputs represent the same physical values. Unit conversions are applied internally. If results shift, double-check that each entered number matches its selected unit.
Between about Re = 2000 and 4000, flow behavior can vary. Treat the friction factor as an estimate, perform sensitivity checks, and validate against measured data when available.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.