Pressure Drop Calculator
Calculate the pressure drop and head loss for fluid flowing through a pipe, using the Darcy-Weisbach equation.
- Free to use
- Accurate results
- No registration required
- Works on all devices
Enter your pipe's dimensions and fluid properties to find the pressure drop and head loss due to friction.
1000 kg/m³ for water at room temperature.
0.001 Pa·s for water at room temperature.
0.045mm is typical for new commercial steel pipe; PVC is smoother (~0.0015mm).
Your result
87.955
Pressure drop
Head loss8.966
Reynolds number1,00,000
Darcy friction factor0.022
AI explanation
Formula
ΔP = f × (L/D) × (ρV²/2) (Darcy-Weisbach); f from 64/Re (laminar) or the Swamee-Jain approximation (turbulent)Worked example
50mm pipe, 100m long, 2 m/s water flow
| Field | Value |
|---|---|
| Pipe internal diameter (mm) | 50 |
| Pipe length (m) | 100 |
| Flow velocity (m/s) | 2 |
| Fluid density (kg/m³) | 1000 |
| Fluid viscosity (Pa·s) | 0.001 |
| Pipe roughness (mm) | 0.045 |
| Reynolds number | 100000 |
| Darcy friction factor | 0.02199 |
| Pressure drop | 87.955 |
| Head loss | 8.966 |
Assumptions
- Uses the explicit Swamee-Jain approximation for the turbulent friction factor (avoiding an iterative Colebrook solve), which is accurate to within about 1% across the normal engineering range.
- Accounts for pipe friction loss only — does not include minor losses from fittings, valves, bends, or entrance/exit effects.
Frequently asked questions
What is the Darcy-Weisbach equation used for?
It's the standard equation for calculating pressure loss due to friction as fluid flows through a pipe, used throughout mechanical, civil, and plumbing engineering.
Why does this calculator use the Swamee-Jain approximation instead of Colebrook?
The Colebrook equation for turbulent friction factor is implicit (it requires iterative solving); Swamee-Jain gives a direct, explicit formula that's accurate to within about 1% — accurate enough for engineering estimates without the complexity of iteration.
Does this include losses from fittings and valves?
No — this calculates straight-pipe friction loss only. Fittings, valves, and bends add additional "minor losses" not included here.