Pipe Pressure Drop Calculator
The Darcy–Weisbach equation estimates frictional pressure loss along a straight pipe from flow velocity, length, diameter, density and friction factor. This is an engineering estimate rather than a complete piping design.
How to use this calculator
- Use internal diameter and a friction factor appropriate to the pipe and flow regime.
- Check that the input values use the same units and reporting period before comparing scenarios.
- Change one assumption at a time to see which input drives the result.
Formula and method
Head loss = f × (L/D) × v²/(2g); pressure loss = density × g × head loss.
- Flow rate is converted to m³/s; velocity is computed from cross-sectional area, then the Darcy–Weisbach head and pressure losses follow.
- Fittings, valves, elevation, temperature, roughness variation, transitional flow and changing fluid properties may add losses. Use qualified engineering review for safety-critical systems.
Worked examples
Worked example
Water-like fluid at 4.5 m³/h through 45 m of 50 mm internal-diameter pipe, with friction factor 0.03.
Flow rate is converted to m³/s; velocity is computed from cross-sectional area, then the Darcy–Weisbach head and pressure losses follow.
The output gives estimated velocity, friction head and pressure loss for the entered assumptions.
Understanding the result
The output gives estimated velocity, friction head and pressure loss for the entered assumptions.
Fittings, valves, elevation, temperature, roughness variation, transitional flow and changing fluid properties may add losses. Use qualified engineering review for safety-critical systems.
Important notes
Use internal diameter and a friction factor appropriate to the pipe and flow regime.
The displayed result uses the entered assumptions; validate important estimates against source measurements, specifications or qualified guidance.
Frequently asked questions
Does this include elbows and valves?
No. Add equivalent-length or loss-coefficient calculations for fittings and components.
Can I use it for every fluid?
The formula accepts density, but viscosity and flow regime still affect the friction factor.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.