Container number check digit validator
Type or paste container numbers to check the ISO 6346 check digit, or enter the first ten characters to calculate the last one. Paste a whole list to check many at once, and add a size and type code such as 45G1 to decode it.
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The formula, in plain terms.
- A container number has 11 characters: a 3-letter owner code, a category letter (U, J or Z), a 6-digit serial number and a check digit.
- Letters become numbers: A = 10, B = 12, C = 13 and so on, skipping multiples of 11 (so L = 23 and V = 34). Digits keep their value.
- Each of the first ten values is multiplied by 2 raised to its position (1, 2, 4, 8 ... 512) and the products are added.
- Divide the total by 11. The remainder is the check digit, and a remainder of 10 is written as 0.
- The size and type code has four characters: length, height and two for the type. For example 45G1 is a 40 ft, 9 ft 6 in high, general-purpose container.
CSQU3054383: C = 13, S = 30, Q = 28, U = 32, then 3, 0, 5, 4, 3, 8. Multiplying by 1, 2, 4, 8, 16, 32, 64, 128, 256 and 512 and adding gives 6,185. 6,185 ÷ 11 leaves a remainder of 3, which matches the last digit, so the number is valid.
Assumptions and limits
- A correct check digit does not prove a container exists. It catches most typing errors, such as a wrong or swapped digit.
- Owner codes are registered with the Bureau International des Containers (BIC). This tool does not look up the owner.
- A remainder of 10 is written as 0, as the standard describes.
- Size and type codes decode the common lengths (10, 20, 30, 40 and 45 ft), heights and type groups. Other codes exist and are shown as not decoded.
- Nothing you enter is sent anywhere. The check runs in your browser.
Common questions
What is a container check digit?
It is the last digit of an 11-character container number. It is calculated from the other ten characters, so a mistyped or misread number usually fails the check.
How is the container check digit calculated?
Each letter is converted to a number, every character is multiplied by a power of two according to its position, the products are added and the total is divided by 11. The remainder is the check digit, with 10 written as 0.
What do the letters in a container number mean?
The first three letters are the owner code. The fourth is the equipment category: U for freight containers, J for detachable equipment such as generator sets and Z for trailers and chassis. Then come six digits of serial number and the check digit.
What does a code like 22G1 or 45G1 mean?
It is the size and type code. The first character is the length (2 = 20 ft, 4 = 40 ft), the second is the height (2 = 8 ft 6 in, 5 = 9 ft 6 in), and the last two give the type, where G1 is a general-purpose container. So 22G1 is a standard 20 ft box and 45G1 a 40 ft high cube.
Why would a check digit not match?
Usually a typing or reading error: a wrong digit, two digits swapped or a letter misread from a photo. Compare the number with the door of the container or the booking document.
Can I check many container numbers at once?
Yes. Paste a list with one number per line or separated by commas and the tool checks each one, showing which are valid, which are wrong and what the correct last digit should be.
Stop re-keying container numbers.
Intelicargo carries container numbers from booking to delivery and flags free time that is about to expire.