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Fanno Flow Calculator — Frictional Compressible Duct Ratios
Calculate Fanno-line property ratios and the remaining friction parameter to sonic choking from Mach number and specific-heat ratio.
Last updated: September 17, 2026
Results
Formula, example and assumptions
4fL*/D=(1−M²)/(γM²)+(γ+1)/(2γ)·ln[((γ+1)M²)/(2+(γ−1)M²)].
For air at M=0.5 the positive remaining friction parameter shows how much constant-area duct friction can be added before M reaches 1.
- Steady adiabatic one-dimensional constant-area ideal-gas flow.
- The reported friction parameter follows the standard 4fL/D Fanno convention.
Frequently asked questions
What does this Fanno Flow Calculator solve?
Calculate Fanno-line property ratios and the remaining friction parameter to sonic choking from Mach number and specific-heat ratio.
Which units should I use?
Use the units printed beside each input. Dimensionless ratios need no conversion; pressure inputs used in gas equations are absolute unless the field explicitly says differential.
Is this suitable for final engineering design?
Use it for transparent first-pass calculations and cross-checks. Final design should verify gas or fluid properties, geometry, loss data, equipment curves and the applicable engineering standard.