Drawing No. EH–FM–014 // Fluid Mechanics & Piping

Pipe Flow & Head Loss Calculator

Reviewed August 2026

Calculate pipe head loss, pressure drop, velocity and Reynolds number using Darcy–Weisbach or Hazen–Williams, including fittings and other minor losses.

Inputs

Hazen–Williams: intended for water in full pressurized pipes, normally under turbulent flow. Use Darcy–Weisbach for other liquids or viscosity-sensitive calculations.

Flow rate, Q m³/h

Internal diameter, D mm

Use actual bore, not nominal size or outside diameter.

Pipe length, L m

Pipe material / Hazen C-factor

Indicative values only; use project, utility, manufacturer or measured data for design.

Minor-loss method

Fittings and valves allowance % of straight-pipe loss

Convenient for early estimates; total K is more physically transferable.

Results

Method: Hazen–Williams · water-service screening

Flow velocity—

Reynolds number—

Flow regime—

Hazen C-factor—

Straight-pipe friction loss—

Minor loss—

Total dynamic loss—

Pressure loss—

Hydraulic gradient—

Hazen–Williams

Use for quick estimates of water flow in full pressurized pipes. The empirical C-factor represents pipe condition. It is not suitable for gases, arbitrary liquids or laminar flow.

Darcy–Weisbach

Use when viscosity and pipe roughness matter. It applies more generally to liquids and handles laminar and turbulent regimes through the friction factor.

Model boundary

The result is dynamic hydraulic loss only. Static elevation, boundary-pressure differences, pumps, water hammer, networks and partially filled pipes are outside this calculation.