The column length (L) divided by the plate number: \[H=\frac{L}{N}\] It is also called the height equivalent to one theoretical plate (
HETP).
Source:
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 848 (https://doi.org/10.1351/pac199365040819)