All Container Equipment Specifications 10 Units
What is ISO 6346?
ISO 6346 is the international standard for identifying and marking shipping containers. It defines the container number, the check digit that protects it against typing errors, and the size-and-type code printed on every box. Owner codes are registered with the Bureau International des Containers (BIC) in Paris, which keeps the global register.
How to read a container number
| Part | Example | Meaning |
|---|---|---|
| Owner code | MSC | Three letters registered to the container owner with BIC |
| Category identifier | U | U = freight container, J = detachable freight-container-related equipment, Z = trailer or chassis |
| Serial number | 123456 | Six digits chosen by the owner |
| Check digit | 7 | Calculated from the first ten characters to catch errors |
Together the owner code and category letter form the four-letter prefix, such as MSCU or MAEU, which tells you who owns the box. See the shipping line directory for each carrier's prefixes.
How the check digit is calculated
- Convert each letter to a number: A = 10, B = 12, C = 13 and so on, skipping 11, 22 and 33 (the multiples of 11). Digits keep their own value.
- Multiply each of the first ten characters by 2 raised to its position (1, 2, 4, 8 … 512).
- Add the results, divide by 11 and take the remainder. That remainder is the check digit; a remainder of 10 becomes 0.
- If the digit you calculate does not match the one on the container or the bill of lading, the number has been copied wrongly.
Size and type codes
| Code | Container |
|---|---|
| 22G1 | 20ft standard dry, 8ft 6in high |
| 42G1 | 40ft standard dry, 8ft 6in high |
| 45G1 | 40ft high cube dry, 9ft 6in high |
| L5G1 | 45ft high cube dry, 9ft 6in high |
| 22R1 | 20ft reefer |
| 45R1 | 40ft high cube reefer |
| 22U1 | 20ft open top |
The first character is the length (2 = 20ft, 4 = 40ft, L = 45ft), the second the height and width (2 = 8ft 6in, 5 = 9ft 6in high cube) and the last two the type (G = general purpose, R = reefer, U = open top). Full specifications for each type are in the container types and dimensions library.
Other markings: CSC plate and VGM
- CSC safety approval plate. Required by the International Convention for Safe Containers (CSC). It shows the maximum gross mass, the stacking and racking values the box was tested to, and the owner's examination scheme.
- Maximum gross mass. Also painted on the door. It is the absolute limit for container plus cargo.
- Verified Gross Mass (VGM). Since 1 July 2016 the SOLAS convention requires the shipper to declare the verified gross mass of every packed export container before it is loaded, either by weighing the packed container (method 1) or by weighing all contents and adding the tare (method 2).
Frequently asked questions
What does the U in a container number mean?
It is the equipment category identifier. U means a freight container, J means detachable equipment related to a container (such as a clip-on generator) and Z means a trailer or chassis.
How do I check if a container number is valid?
Calculate the check digit from the first ten characters using the ISO 6346 method: convert letters to numbers, weight each position by powers of two, sum, divide by 11 and take the remainder. It must match the last digit.
Who assigns container owner codes?
The Bureau International des Containers (BIC) in Paris registers owner codes under ISO 6346 and keeps the global database of prefixes.
What does 45G1 mean on a container?
45G1 is the size-type code for a 40ft high cube general-purpose container: 4 = 40ft long, 5 = 9ft 6in high, G1 = general purpose with vents.
What is VGM in shipping?
Verified Gross Mass: the total weight of the packed container, which the shipper must declare before loading under the SOLAS convention, in force since 1 July 2016.