Darcy–Weisbach Headloss

Compute friction factor, Reynolds number, and headloss (major + minor). Also solve diameter for a target headloss.

Inputs

Mode

Flow rate Q (m³/s)

Pipe length L (m)

Absolute roughness ε (m)

Kinematic viscosity ν (m²/s)

Minor losses ΣK (–)

Gravity g (m/s²)

Diameter D (m) (disabled in diameter mode)

Target total headloss h_tot (m) (used in diameter mode)

Outputs

Velocity v (m/s)

Reynolds number Re (–)

Friction factor f (–)

Major headloss h_f (m)

Minor losses h_m (m)

Total headloss h_tot (m)

Pressure drop Δp (kPa)

Solved diameter D (m)

Tips: Use ε≈0.000045 for new steel, ν≈1.0e−6 m²/s at 20 °C water. Sum K for bends/valves if needed. Δp uses ρ=1000 kg/m³.