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Diagram of container rear doors with callouts identifying the classification mark, owner's logo, repair recommendation, combined data plate, container number, maximum gross weight, tare weight, maximum payload, capacity, height warning, and manufacturer's logo.

Container Knowledge Center

How to Read Container Numbers & Markings

Shipping containers display standardized identification markings that help operators, terminals, logistics providers, and other supply-chain participants identify equipment and validate container numbers. This guide explains the main elements buyers may see on an international freight container.

Diagram of container rear doors with callouts identifying the classification mark, owner's logo, repair recommendation, combined data plate, container number BICU 123456 7, maximum gross weight, tare weight, maximum payload, capacity, height warning, and manufacturer's logo.
Marking requirements vary by shipment and carrier. This graphic is an educational example, for reference only.
Graphic decoding the first two digits of a container size and type code: first digit is length, where 2 equals 20 feet and 4 equals 40 feet; second digit is height, where 2 equals 8 feet 6 inches standard and 5 equals 9 feet 6 inches high cube, with examples 22, 25, 42, and 45.
Reading the first two digits. The first digit gives the length and the second gives the height, so codes such as 22, 25, 42, and 45 describe the box at a glance.
Common ISO general-purpose container size and type codes: 22G1, 22G2, 25G1, 25G2, 42G1, 42G2, 45G1, 45G2.
Common ISO general-purpose size/type codes. The first two digits indicate size, the third indicates height, and the fourth indicates the characteristic.
G1 and G2 container codes: G1 = passive upper vents, G2 = full side openings.
The final two characters in a size/type code describe construction characteristics. G1 and G2 refer to vent and opening configurations, rather than a universal vent count.

ISO 6346 reference

Size & type code tables

The size and type code is a four-character sequence shown under the container identification number. The first character gives the length, the second gives the height (and width), and the last two identify the container type and its characteristics.

First character — length
CodeLength
220 feet
440 feet
545 feet
M48 feet
Second character — height
CodeHeight
28 feet 6 inches
59 feet 6 inches (High Cube)
Third & fourth characters — type
CodeContainer type
G1General purpose container
R1Refrigerated container
U1Open top container
P1Platform / flat rack container
T1Tank container
Full length code table (ISO 6346, Table 1)
CodeLength (mm)Length (ft / in)
1299110 ft
2605820 ft
3912530 ft
41219240 ft
51371645 ft
A7150—
B731524 ft
C743024 ft 6 in
D7450—
E7820—
F8100—
G1250041 ft
H1310643 ft
K13600—
M1463048 ft
N1493549 ft
P1615453 ft
Full height code table (ISO 6346, Table 2 — width 2438 mm)
CodeHeight (mm)Height (ft / in)
024388 ft
225918 ft 6 in
427439 ft
528969 ft 6 in
6> 2896> 9 ft 6 in
812954 ft 3 in
9≤ 1219≤ 4 ft
Containers with reduced stacking and racking strength are marked with a letter in the fourth position. Source and current standard: bic-code.org/size-type-code. Refer to the latest version of ISO 6346 for complete marking requirements.

The identification sequence

What each element means

  • Owner Prefix

    The owner prefix is a three-letter code that identifies the container owner or principal operator.

  • Equipment Category Identifier

    The equipment category identifier is one letter. “U” is used for freight containers.

  • Serial Number

    The serial number is a six-digit number selected by the owner or operator to identify the container within its equipment fleet.

  • Check Digit

    The check digit is a one-digit validation tool used to help detect recording or transmission errors in the container number.

  • Size & Type Code

    The size and type code helps identify the container’s size, height, type, and characteristics. For example, size/type codes are commonly displayed near the main identification sequence.

Marking and documentation requirements vary by shipment, carrier, cargo, route, and applicable regulations. Confirm the requirements for the specific shipment with the carrier, forwarder, or Pro Box team.
Owner prefixes and ISO size/type codes are managed by the Bureau International des Containers (BIC). For more information, please visit bic-code.org.
Reviewed by Pro Box Inc. technical teamLast reviewed: September 2026

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