The format of an ILU code
An ILU code is four letters, six digits and one check digit. The fourth letter is the category and is A, B, D, E or K — distinguishing intermodal loading units from ISO 6346 containers, which use U, J or Z. The owner is identified by the first three letters, registered in the ILU register operated by UIRR.
Relationship to the ISO 6346 container code
UIRR, which manages the ILU register, describes the ILU code as fully compatible with the BIC code used for maritime containers under ISO 6346, and refers to a defined procedure for the check digit. Checkdigit routes categories A, B, D, E and K to the ILU set and checks them with the same mod-11 arithmetic as ISO 6346.
That arithmetic has not been independently verified here against the normative EN 13044-1 text, so this is a statement of compatibility, not a claim of normative compliance. The calculator labels ILU results accordingly.
Where you will see ILU codes
ILU codes appear on swap bodies and intermodal units in European rail and combined transport, alongside container numbers and, on rail vehicles, UIC wagon numbers.