Container number structure

OWL3-letter owner code (BIC-registered).
UEquipment category — U for freight containers (the common case), J for detachable freight-related equipment, Z for trailers and chassis.
1234566-digit serial (owner-assigned).
3Check digit (computed from the first 10 characters).

The algorithm in five lines

Look up each of the first 10 characters' value (letters per the table below, digits are themselves).
Multiply each value by 2 to the power of its position (positions 0–9).
Sum all ten products.
Take that sum modulo 11.
The remainder modulo 10 is the check digit. (A remainder of 10 is printed as 0; ISO 6346 recommends not allocating those serials, since single-character errors can slip past the check.)

Letter → integer table

Letters skip multiples of 11 (the gaps before L and V). That guarantees no two letters are congruent mod 11, so a single substitution always changes the check digit.

A=10

B=12

C=13

D=14

E=15

F=16

G=17

H=18

I=19

J=20

K=21

L=23

M=24

N=25

O=26

P=27

Q=28

R=29

S=30

T=31

U=32

V=34

W=35

X=36

Y=37

Z=38

How it works

ISO 6346 defines the check digit, the eleventh character of every container number. Each of the first ten characters becomes a number: digits keep their value, and letters count up from A = 10, skipping 11, 22 and 33. Each value is multiplied by its position weight — 1, 2, 4, 8 and so on up to 512 — and the products are added. The total is divided by 11, and the remainder is the check digit; a remainder of 10 is written as 0.

A wrong check digit almost always means a typo in the number. The calculation runs in your browser; the number you type is not sent anywhere.

Owner names for the first four letters come from our curated list of frequently seen prefixes, including our own OWLU^®, ANYU and LSEU. See the full list on the BIC prefix lookup, or the ISO 6346 guide for the whole numbering system.