| dimensioned variables (metric as example) |
| Δ p | [kg/(m s²) = 10-5 bar = 10-2mbar] | : Pressure loss of the straight pipe |
| l | [m] |
: Length |
| d | [m] |
: Internal Diameter |
| ρ | [kg/m³] | : Density |
| v | [m/s] | : Average speed in the pipe |
| η | [kg/(m s) = Pas] | : Dyn. Viscosity |
| ε | [m] | : Roughness |
| dimensionless values |
| Re | [-] | : Reynolds number Re = ρ v d / η |
| f | [-] |
: Darcy Friction Factor |