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Darcy-Weisbach formula

Fluid dynamics index

The equation states that the pressure loss ΔP=fLρV²/2D (where L and D are th pipe length and diameter, ρ is the fluid density, V is the average velocity through the pipe, and f is the Darcy friction factor).
Head loss is also available through the unit menus.
 Pipe diameter: m --- METRIC --- pm nm microns (µm) mm cm km -- IMPERIAL -- mil 1/16 inch inches feet yards miles - SCIENTIFIC - Planck Bohrs Angstrom light-seconds light-years au parsecs --- OTHER --- points cubits fathoms rods chains football fields furlongs Roman miles nautical miles leagues Pipe length: m --- METRIC --- pm nm microns (µm) mm cm km -- IMPERIAL -- mil 1/16 inch inches feet yards miles - SCIENTIFIC - Planck Bohrs Angstrom light-seconds light-years au parsecs --- OTHER --- points cubits fathoms rods chains football fields furlongs Roman miles nautical miles leagues Velocity: m/s --- METRIC --- cm/s km/s -- IMPERIAL -- inches/second feet/second feet/minute - RECIPROCAL - min/mile min/km min/5 km min/10 km --- OTHER --- km/h mph miles/second knots furl's/f'night Mach c (light speed) Discharge rate: m³/s mL/min liter/min liter/s m³/min cu ft/s cu ft/min gal(US)/min gal(UK)/min Darcy friction factor: Density: kg/m³ g/m³ g/cm³ oz/in³ lb/ft³ Pressure drop: Pa nPa µPa mPa kPa MPa GPa atm kgf/cm²   (at) mbar bar mmHg (Torr) in Hg ft H2O m H2O psi Add

Only either the velocity or the discharge rate needs to be entered. The Darcy friction factor f is also known as the "flow coefficient" λ or the Moody friction factor, and is 4x the Fanning friction factor. It is dependant on many factors such as the pipe material, shape, and fluid velocity. Therefore, it must be known or calculated for each specific use. For laminar flow in a circular pipe, it is 64/Re.
Other calcs designed for specific conditions are available, which do not have the need for a known value of f.