Pressure Drop Calculator Formula

Understand the math behind the pressure drop calculator. Each variable explained with a worked example.

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Formulas Used

Pressure Drop

delta_p = friction_f * (length / d_m) * 0.5 * density * pow(velocity, 2) / 1000

Equivalent Head Loss

head_loss = friction_f * (length / d_m) * pow(velocity, 2) / (2 * 9.81)

Variables

VariableDescriptionDefault
friction_fFriction Factor (f)0.02
lengthPipe Length (L)(m)50
diameterPipe Diameter (D)(mm)80
velocityFlow Velocity (V)(m/s)2.5
densityFluid Density (rho)(kg/m^3)1000
d_mDerived value= diameter / 1000calculated

How It Works

Pressure Drop in Pipes

Pressure drop is the energy lost to friction as fluid flows through a pipe.

Formula

delta_P = f (L/D) (0.5 rho V^2)

This is the Darcy-Weisbach equation expressed in pressure units (Pa) rather than head (m). The two forms are related by delta_P = rho g h_f.

Worked Example

Water at 2.5 m/s through 80 mm pipe, 50 m long, f = 0.02.

friction_f = 0.02length = 50diameter = 80velocity = 2.5density = 1000
  1. 01D = 0.08 m, L/D = 50/0.08 = 625
  2. 02Dynamic pressure = 0.5 x 1000 x 2.5^2 = 3125 Pa
  3. 03delta_P = 0.02 x 625 x 3125 = 39,063 Pa = 39.1 kPa
  4. 04Head loss = 39,063 / (1000 x 9.81) = 3.98 m

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