Darcy-Weisbach Head Loss Calculator

Your details

Choose which quantity to calculate; all other fields are treated as known inputs.
Straight pipe length over which head loss is calculated.
m
Internal diameter of the pipe (not outer diameter).
m
Mean flow velocity of the fluid in the pipe.
m/s
Density of the fluid: water = 1000 kg/m³, air at 20 °C ≈ 1.2 kg/m³.
kg/m³
Kinematic viscosity = dynamic viscosity / density. Water at 20 °C ≈ 1.004×10⁻⁶ m²/s.
m²/s
Absolute roughness of the pipe wall. Commercial steel ≈ 0.046 mm; smooth plastic ≈ 0.0015 mm; cast iron ≈ 0.26 mm.
m
Known head loss used when solving for another unknown.
m
Enter a known Darcy friction factor, or leave 0 to auto-compute from Colebrook-White using roughness and Reynolds number.
Head loss (hf)Turbulent flow
3.796

Energy loss per unit weight of fluid due to pipe friction

Pressure drop (ΔP)37,225.62
Darcy friction factor (f)0.01861
Reynolds number (Re)200,000
Flow regimeTurbulent
Relative roughness (ε/D)0.00046
Flow velocity (v)2
Flow rate (Q)0.0157
Power loss (P)584.74
200,000
Laminar<2300Transitional2300-4000Turbulent4000+

Head loss: 3.796 m - Turbulent flow

  • Flow is turbulent (Re = 200,000). Inertial forces dominate; friction factor depends on both Re and pipe roughness.
  • The Darcy friction factor is 0.0186. Relative roughness ε/D = 0.00046 contributes significantly to friction.
  • Head loss of 3.80 m corresponds to a pressure drop of 37226 Pa.
  • Power consumed by friction: 584.7 W. Reducing pipe roughness or increasing diameter significantly cuts this loss.

Next stepTo reduce head loss: increase pipe diameter (loss scales as D^-5), reduce velocity, shorten the run, or choose a smoother material.

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