Formulas
Coefficient of Friction
C
The coefficient of friction is the number in the friction loss formula that captures a hose's diameter and roughness. Larger hose has a much smaller coefficient, which is why bigger lines lose so little pressure.
Each hose size carries its own coefficient. It is the multiplier that turns flow-squared-times-length into a pressure loss, so it encodes everything about the hose that affects friction — mainly its inside diameter.
Because the coefficient falls sharply as diameter grows, switching to a larger line can cut friction loss dramatically at the same flow. The coefficient is where the 'bigger hose costs less' rule comes from.
Where this shows up
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Friction LossCalculator
Friction Loss Reference Table