Calculator inputs
Example data table
This example uses a 30 m pipe, 50 mm diameter, 3 L/s flow, water-like density, 1 cP viscosity, and 0.045 mm roughness.
| Metric | Example value |
|---|---|
| Pipe Length | 30 m |
| Pipe Diameter | 50 mm |
| Flow Rate | 3 L/s |
| Density | 998 kg/m³ |
| Dynamic Viscosity | 1 cP |
| Absolute Roughness | 0.045 mm |
| Velocity | 1.527887 m/s |
| Reynolds Number | 76,241.58 |
| Friction Factor | 0.0226387 |
| Pressure Drop | 15.822901 kPa |
| Head Loss | 1.61672 m |
Formula used
The calculator uses the Darcy-Weisbach relation for straight-pipe friction losses.
Area = πD² / 4
Velocity = Q / Area
Re = ρVD / μ
ΔP = f × (L / D) × (ρV² / 2)
Head Loss = ΔP / (ρg)
For automatic friction factor, the script uses the Churchill equation. It works across laminar, transitional, and turbulent ranges. Manual mode lets you enter a known friction factor directly.
How to use this calculator
- Enter pipe length and choose its unit.
- Enter internal pipe diameter and its unit.
- Enter flow rate with the unit you use.
- Add fluid density and dynamic viscosity.
- Enter the pipe roughness for the material.
- Select automatic or manual friction factor mode.
- Choose the output pressure unit.
- Press Calculate to see pressure drop, flow regime, head loss, and the trend graph above the form.
FAQs
1) What does this calculator estimate?
It estimates pressure loss caused by wall friction inside a straight pipe. It also reports Reynolds number, velocity, friction factor, roughness ratio, head loss, and flow regime.
2) Which equation does it use?
It uses Darcy-Weisbach for pressure loss. In automatic mode, friction factor comes from the Churchill equation, which handles smooth and rough pipes across different Reynolds number ranges.
3) When should I use manual friction factor mode?
Use manual mode when your design standard, manufacturer data, or test results already provide a trusted Darcy friction factor. This is useful for controlled engineering studies.
4) Does this include fittings and valves?
No. This page focuses on straight-pipe friction loss only. Minor losses from elbows, valves, tees, reducers, and entrances should be added separately in a full system study.
5) Why is Reynolds number important?
Reynolds number helps classify flow as laminar, transitional, or turbulent. That classification affects friction factor behavior and strongly changes the final pressure-drop result.
6) What roughness value should I enter?
Enter the absolute roughness for your pipe material and condition. New smooth tubing and old corroded piping can produce very different results, even at the same flow rate.
7) Why does pressure drop rise quickly with flow?
Velocity rises as flow increases, and friction loss depends strongly on velocity. In many operating ranges, pressure drop increases much faster than flow, especially in turbulent conditions.
8) Can I use this for liquids and gases?
It works best when density and viscosity remain reasonably constant along the pipe. For highly compressible gas systems, a dedicated compressible-flow model is usually better.