Theoretical Plates Calculator
Calculate the number of theoretical plates (N) for your HPLC column using the USP <621> tangent method — enter retention time and peak width for an instant plate count.
Theoretical plates (N) are the standard measure of an HPLC column’s separating efficiency. A higher plate count means sharper peaks and better resolution between closely eluting compounds — and tracking it over a column’s lifespan is one of the simplest ways to know when performance has started to degrade.
This calculator uses the USP General Chapter 621 tangent method, N = 16(tR/W)², where tR is the peak’s retention time and W is its width at baseline. Enter both values in the same time units and the calculator returns N rounded to the nearest whole number, the convention used throughout USP general chapters and most chromatography data systems.
For the underlying concept — why theoretical plates matter, how HETP relates to column efficiency, and what factors affect plate count — see Concept of Theoretical Plates in Column Chromatography.
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