Overall distillation column efficiency for most of the refinery columns can be given by (for μ = 0.07 - 1.4 cp and relative volatility < 4) (where η = overall column efficiency, % μ = molal average viscosity of feed at average column temperature and pressure, cp Δp = pressure drop per tray, psi)

• η = 17 - 61.1 log μ
• η = 1.66 - 0.25 log μ
• η = 0.25 log μ - 1.67