Fluid & Piping

Straight Pipe Friction Loss Calculator

Estimate Darcy-Weisbach friction head and pressure loss for a straight pipe run, with velocity, Reynolds number and friction factor shown.

“I know the flow, bore and length. How much pressure will I lose through the straight pipe before fittings and elevation are added?”

Core formulae

Straight-pipe friction reference

Average velocityv = Q / A

Reynolds numberRe = ρ v D / μ

Darcy-Weisbach lossh_f = f (L/D) (v² / 2g)

Pressure lossΔP = ρ g h_f

This quick tool excludes fittings, valves, entrances, exits and static elevation. Use the full Pipe Pressure Drop calculator for the complete system requirement.

Simple arrangement sketch

Straight pipe run

Enter the straight pipe run

This quick calculator isolates straight-pipe friction. Use the full pressure-drop calculator when fittings, valves, static head or pump margin matter.

Flow rateFlow unitActual internal diametermmUse the real bore, not nominal DN alone.Straight pipe lengthm

Set pipe roughness and fluid properties

Use presets as starting points, then override the values when better project data are available.

Pipe roughness starting pointAbsolute roughnessmmFluid presetFluid densitykg/m³Dynamic viscositymPa·s1 mPa·s = 1 cP. Use dynamic viscosity, not kinematic viscosity in cSt.

Results

Straight-pipe friction only

Pressure loss58.3 kPa

Friction head loss5.95 m

Average velocity2.55 m/s

Reynolds number253,685

Turbulent

Darcy friction factor0.018

Relative roughness0.00045

Velocity screening flag not triggered

The calculator does not establish an acceptable velocity range for your service. Confirm the project, material and fluid-specific criteria.

Method

Darcy-Weisbach straight-pipe loss only. Friction factor uses the same laminar / Haaland model as the main Pipe Pressure Drop calculator for consistent results across AS Applied.

Job-file record

Save the calculation, not just the number.

Copy a permalink that reloads these inputs, or download a PDF record with inputs, visible results, assumptions, a sensitivity note, date and disclaimer.

Why this matters

What the result helps you understand

Straight-pipe loss can consume a large part of the available pressure or pump head before fittings and elevation are added. A quick friction screen helps identify when pipe bore is driving the system requirement.

What this does not cover

Know where the quick calculation stops

This calculator excludes fittings, valves, entrances, exits, static elevation, transients and ageing effects. Use the full Pipe Pressure Drop calculator for a system-level head requirement.

Important boundary

A calculator can show the arithmetic. It cannot establish every requirement that applies.

Confirm the actual equipment, loading, materials, condition, jurisdiction, contractual requirements, standard edition and current project documentation before using the result for design, repair, testing or lifting decisions.

Ask an engineer about this calculation →