How this calculation works
Apply the straight-pipe Darcy multiplier and entered fitting coefficient to the same velocity pressure. Add the resulting losses, then convert pressure loss to fluid head or hydraulic dissipation.
Δp = (fD·L/D + ΣK)ρv²/2; head loss = Δp/(ρg)A worked example
With Darcy factor 0.02, length 10 m, diameter 100 mm, velocity 2 m/s, density 1,000 kg/m³ and K = 1, the modeled pressure loss is 6,000 Pa.
Good to know
Enter a Darcy factor, not an unconverted Fanning factor. No roughness inference, gas compressibility, elevation term or real-system design approval is included. Every fitting coefficient must match the stated reference velocity.
Reference: US Department of Energy: fluid flow and head losses (opens in a new tab) ↗
Loss multipliers share a velocity-pressure basis
The default dynamic pressure is ½×1,000×2² = 2,000 Pa. The straight-pipe multiplier is 0.02×10/0.1 = 2, and the entered fitting multiplier is 1. Their total of 3 gives 6,000 Pa modeled loss.
Keeping these components separate makes a change interpretable. Doubling the entered length doubles only the straight-pipe component; the unchanged fittings retain their original contribution at the same velocity.
The Venturi flow calculator uses an acceleration-related tap pressure difference; it is not a substitute for an irreversible friction-loss calculation.
Darcy and Fanning factors differ by four
The formula here expects the Darcy friction factor. A Fanning factor for the same flow is one quarter of the Darcy factor, so it must be multiplied by four before entry. Confusing the names creates a fourfold error in the straight-pipe contribution.
The pipe Reynolds number calculator can help characterize the flow, but it does not automatically supply a turbulent factor. This page accepts a factor obtained from an appropriate calculation, reference or measurement.
Pressure difference is not always dissipated loss
Elevation changes and changes in flow speed can change static pressure without being irreversible friction losses. This page sums only the entered pipe and fitting loss model. The Venturi flow calculator uses a pressure difference related to acceleration, which is a different task.
Every fitting coefficient must use the same reference velocity entered here. Combining coefficients defined at different pipe sections without conversion can produce an inconsistent total. Compressible gases and variable-density flow also require additional treatment.
A few questions, answered
Can I enter a Fanning factor directly?
No. Convert it to the Darcy convention by multiplying by four.
Does zero pipe length mean zero total loss?
Only when the entered fitting coefficient is also zero, or the velocity is zero.
What does hydraulic dissipation mean?
It is modeled pressure loss times volume flow. It is not electrical motor input power.