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Darcy pipe friction loss
Estimate straight-pipe pressure loss using a flow-regime-aware Darcy factor.
A clear answer. Here’s how.
Calculates velocity and Reynolds number, then uses f=64/Re below Re 2,000 and the Swamee–Jain approximation above Re 4,000. Transitional values are rejected rather than interpolated. Relative roughness is bounded to 0.05. Darcy–Weisbach head loss=f(L/D)V²/(2g); pressure loss=ρg×head. Fully filled steady circular pipe only; fittings, elevation and fluid property variation are excluded.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Internal diameter (mm)
- 25
- Volume flow (L/min)
- 20
- Straight pipe length (m)
- 10
- Fluid density (kg/m³)
- 1000
- Dynamic viscosity (mPa·s)
- 1
- Absolute roughness (mm)
- 0.01
Example result
- Mean velocity (m/s)
- 0.679061090525
- Reynolds number
- 16,976.5272631
- Darcy friction factor
- 0.0278064740104
- Friction head loss (m)
- 0.261500747738
- Pressure loss (kPa)
- 2.56444630781
- Flow model
- Turbulent, Swamee–Jain approximation
Straight, fully filled circular pipe only. Darcy factor is four times the Fanning factor; fittings and elevation are excluded.