HPLC Column Backpressure Calculator with Mobile Phase Viscosity

Estimate column pressure before you switch to smaller particles or a higher flow.

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Column length mm

Column ID mm

Particle size µm

Flow mL/min

Organic solvent

Organic in water % v/v

Column temperature °C

Estimate for a fully porous packed column, typically within ±30%. Superficially porous and monolithic columns run lower.

Viscosity–

Pressure–

ΔP (bar) ≈ 380 · F·η·L/(dp²·dc²) with F in mL/min, η in cP, L in mm, dp in µm, dc in mm

How it works

Column pressure follows Darcy's law: it rises in proportion to flow, viscosity and column length, and with the inverse square of particle size and column diameter. Halving the particle size at the same flow therefore quadruples the pressure.

Water–methanol mixtures are much more viscous than water–acetonitrile, peaking at about 1.6 cP near 40–50% methanol at 25 °C, so a methanol gradient passes through a pressure maximum mid-run. Raising the temperature by 20 °C lowers viscosity by roughly a third.