What is the container number check digit?

It is the 11th character of an ISO 6346 container number — a single digit computed from the first 10 characters (the 4-letter owner+category code and the 6-digit serial). It lets any system catch a mistyped container number before it is used.

How is the check digit calculated?

Each of the first 10 characters is converted to a value (digits map to themselves; letters use the ISO 6346 table where A=10, B=12 … Z=38, skipping multiples of 11). Each value is multiplied by 2 raised to its position (1, 2, 4, 8 … 512), the products are summed, and the sum is taken modulo 11. If the remainder is 10 it becomes 0 — that remainder is the check digit.

What does an invalid check digit mean?

Almost always a typo — a swapped or mistyped character. A carrier site will reject the number too. Re-read the number from the container or the bill of lading and try again.

Does a valid check digit mean the container exists?

No. The check digit only proves the number is internally consistent (not mistyped). Whether that container is in service, and where it is, depends on the shipping line — paste it into TrackJet and we route you to the carrier’s official tracking surface.

Container number check digit calculator (ISO 6346)

Paste a shipping-container number and this tool validates the ISO 6346 check digit — the 11th character that catches a mistyped number before a carrier ever sees it. It shows the full calculation, so you can see why a number is valid or not, and routes a valid number straight to official tracking.

What the check digit is

A standard container number under ISO 6346 is 11 characters: a 3-letter owner code (registered with the BIC), a 1-letter category (U freight container, J detachable chassis, Z trailer/chassis), a 6-digit serial, and a final check digit. The check digit is not random — it is computed from the other ten characters, so a single mistyped character almost always produces a number that fails the check. That is exactly what this calculator verifies.

How it is calculated

Convert each of the first 10 characters to a value. Digits map to themselves; letters use the ISO 6346 table below (note 11, 22 and 33 are skipped).
Multiply each value by 2 raised to its position — weights 1, 2, 4, 8, 16, 32, 64, 128, 256, 512.
Add the products together.
Take the sum modulo 11. The remainder is the check digit — except a remainder of 10 becomes 0.

ISO 6346 letter values

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

Worked example: CSQU3054383

This is the worked example in the ISO 6346 standard itself. C=13, S=30, Q=28, U=32, then the serial 3 0 5 4 3 8. Multiply by the weights, sum to 6185, and 6185 mod 11 = 3 — so the check digit is 3, matching the final character. Paste it into the tool above to see every row.

Why a number may still not track

A valid check digit only means the number is internally consistent. It does not prove the container is in service or that a shipping line is publishing its position. TrackJet detects the format, identifies the line from the owner code and routes you to the official tracking surface; where a licensed feed or user-authorised source exists it builds a source-labelled timeline, and it never fabricates events.

FAQ

What is the container number check digit?: It is the 11th character of an ISO 6346 container number — a single digit computed from the first 10 characters (the 4-letter owner+category code and the 6-digit serial). It lets any system catch a mistyped container number before it is used.
How is the check digit calculated?: Each of the first 10 characters is converted to a value (digits map to themselves; letters use the ISO 6346 table where A=10, B=12 … Z=38, skipping multiples of 11). Each value is multiplied by 2 raised to its position (1, 2, 4, 8 … 512), the products are summed, and the sum is taken modulo 11. If the remainder is 10 it becomes 0 — that remainder is the check digit.
What does an invalid check digit mean?: Almost always a typo — a swapped or mistyped character. A carrier site will reject the number too. Re-read the number from the container or the bill of lading and try again.
Does a valid check digit mean the container exists?: No. The check digit only proves the number is internally consistent (not mistyped). Whether that container is in service, and where it is, depends on the shipping line — paste it into TrackJet and we route you to the carrier’s official tracking surface.