Pipe Pressure Drop Calculator

Calculate pipe friction pressure drop using the Darcy-Weisbach equation with Swamee-Jain friction factor. Handles laminar, transition, and turbulent flow regimes.

Inputs

Volumetric flow rate (m³/hr)

Pipe inner diameter (mm)

Pipe length (m)

Pipe roughness ε (mm)

Fluid density (kg/m³)

Dynamic viscosity (Pa·s)

Tab to move between fields

Results

Pressure drop (kPa)

1.49

Flow velocity (m/s)

0.35

Pressure drop (bar)0.01

Pressure drop (psi)0.22

Reynolds number35,297

Darcy friction factor0.02

Head loss (m)0.15

Velocity head (m)0.01

Flow RegimeTurbulent

How to Use This Calculator

Enter Volumetric flow rate (m³/hr), Pipe inner diameter (mm), and Pipe length (m).
Set Pipe roughness ε (mm), Fluid density (kg/m³), and Dynamic viscosity (Pa·s).
Review Pressure drop (kPa) and Flow velocity (m/s).
Use Pressure drop (bar) and Pressure drop (psi) to inform your decision.

How the result changes with Pipe inner diameter (mm)

Pipe inner diameter (mm)	Pressure drop (kPa)	Flow velocity (m/s)
501	0	0.01
1,751	0	0
3,250	0	0
4,500	0	0

What each input means

Volumetric flow rate (m³/hr): Fluid volumetric flow rate through the pipe.
Pipe inner diameter (mm): Internal diameter of the pipe.
Pipe length (m): Total equivalent length of straight pipe.
Pipe roughness ε (mm): Absolute roughness: steel ≈ 0.045 mm, copper ≈ 0.0015 mm, PVC ≈ 0.0015 mm.
Fluid density (kg/m³): Water ≈ 998, air ≈ 1.2, oil ≈ 850 kg/m³.
Dynamic viscosity (Pa·s): Water at 20°C ≈ 0.001 Pa·s, oil ≈ 0.1–1 Pa·s.

What each result means

Pressure drop (kPa): Total friction pressure loss along the pipe.
Pressure drop (bar): Pressure drop in bar.
Pressure drop (psi): Pressure drop in pounds per square inch.
Flow velocity (m/s): Average fluid velocity in the pipe.
Reynolds number: Dimensionless number indicating flow regime (<2300 laminar, >4000 turbulent).
Darcy friction factor: Dimensionless friction factor from Swamee-Jain (turbulent) or 64/Re (laminar).
Head loss (m): Pressure drop expressed as meters of fluid column.
Velocity head (m): v²/(2g) — useful for fitting loss calculations.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Volumetric flow rate (m³/hr) = 10, Pipe inner diameter (mm) = 100, Pipe length (m) = 100, Pipe roughness ε (mm) = 0.045 = 6 input(s) provided
Calculate Pressure drop
Pressure drop = deltaPPa / 1000
1.49 = 1.49
Calculate Flow velocity
Flow velocity = Q / A
0.3537 = 0.3537
Calculate Pressure drop
Pressure drop = deltaPPa / 100000
0.0149 = 0.0149
Calculate Pressure drop
Pressure drop = deltaPPa * 0.000145038
0.22 = 0.22