HPLC Column Scaling Calculator: Flow Rate, Injection Volume & Gradient Time

Scale flow, injection volume and gradient time when column dimensions change.

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Original length mm

New length mm

Original ID mm

New ID mm

Original particle µm

New particle µm

Original flow mL/min

Original injection µL

Original gradient time min

Example: 150 × 4.6 mm, 5 µm moved to 100 × 3.0 mm, 3 µm.

New flow–

New injection–

New gradient time–

L/dp change–

F₂ = F₁·(d₂²·dp₁)/(d₁²·dp₂) · V₂ = V₁·(L₂d₂²)/(L₁d₁²) · tG₂ = tG₁·(F₁/F₂)·(L₂d₂²)/(L₁d₁²)

How it works

Flow is scaled with the square of the column diameter so the linear velocity stays the same, and inversely with particle size so the reduced velocity stays near the van Deemter optimum. Injection volume scales with column volume to keep the same relative loading.

For gradients, keeping the gradient volume constant in column volumes keeps k* constant and preserves selectivity. Since USP <621> was harmonised, both isocratic and gradient methods can be adjusted when L/dp stays within −25% to +50%, subject to system suitability.