For turbulent flow (NRe > 2100) of low viscosity fluid (μ > 20cp) in steel pipes, the optimum inside pipe diameter is given by(where, Q = fluid flow rate, ft3/sec.ρ = fluid density, lb/ft3 μ = fluid viscosity, centipoise Di = optimum inside pipe diameter, inches)

• Di, opt = 3.9 Q0.45 ρ0.13
• Di, opt = 3.9 Q0.45 . μ0.95
• Di, opt = 4.7 Q0.36 . μ3.2ρ0.13
• Di, opt = 3 Q0.36 . μ0.88