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Darcy-Weisbach Pipe Pressure Loss

Calculate velocity, friction head loss and pressure drop in a straight circular pipe.

Updated September 2026

How it works

Calculate velocity, friction head loss and pressure drop in a straight circular pipe.

Formula:
v = Q/A; hf = f·(L/D)·v²/(2g); Δp = ρg·hf.

Before you use the result: Minor losses from fittings, valves and equipment are not included.

Practical use

Use verified material data and project geometry. Treat results as planning estimates and compare them with the energy/thermal requirements that apply to the project.

Keep units consistent with the source information.
Use project-specific densities, pack sizes and coverage rates where provided.
Round purchasing quantities to supplier packaging and delivery rules.

How to use this calculator: Darcy-Weisbach Pipe Pressure Loss

Calculate velocity, friction head loss and pressure drop in a straight circular pipe.

Quick workflow

Enter the project values from the latest drawing, specification or verified site measurement.
Check units, material properties, allowances and any code- or supplier-specific parameters before calculating.
Review the result together with the formula, assumptions and the related checks shown on this page.

Worked example

Example inputs: Flow rate [L/s]: 5; Inside diameter [mm]: 65; Straight pipe length [m]: 40; Darcy friction factor f: 0.022.

Using the sample values built into the calculator, the calculation gives approximately: Fluid velocity: 1.507 m/s; Friction head loss: 1.567 m; Pressure loss: 15.37 kPa.

What the result means

Calculation method: v = Q/A; hf = f·(L/D)·v²/(2g); Δp = ρg·hf.

Before using the result: Minor losses from fittings, valves and equipment are not included.

Common questions

What does this calculator do?

Calculate velocity, friction head loss and pressure drop in a straight circular pipe.

Which inputs should I verify?

Key inputs to verify include: Flow rate [L/s], Inside diameter [mm], Straight pipe length [m], Darcy friction factor f.

Can I use this result for final design or ordering?

Use the result as a transparent planning or checking aid. Final design, code compliance, supplier selection and project-specific decisions still need to be verified where applicable. Minor losses from fittings, valves and equipment are not included.

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