Every container carries two key identities: an ISO 6346 container number (for example CSQU 305438 3) that is unique to that one unit, and a size-type code (for example 22G1) that describes its length, height and type. This guide covers the container types most used for shipments to and from Indonesia, how to read a container number and how to work out the check digit step by step.
The most common container types
| Type | Typical code | Internal volume | Best for |
|---|---|---|---|
| 20ft dry (20GP) | 22G1 | 33.2 m³ | Dense cargo, small volumes |
| 40ft dry (40GP) | 42G1 | 67.7 m³ | General cartons and pallets |
| 40ft high cube (40HC) | 45G1 | 76.4 m³ | Light, bulky cargo |
| 45ft high cube (45HC) | L5G1 | 86.0 m³ | Selected lanes only |
| 20ft reefer | 22R1 | 28.4 m³ | Frozen and chilled food |
| 40ft reefer high cube | 45R1 | 67.7 m³ | Food, pharma, fresh fruit |
| 20ft / 40ft open top | 22U1 / 42U1 | 32.6 / 66.4 m³ | Tall cargo, top loading |
| 20ft / 40ft flat rack | 22P1 / 45P1 | no side walls | Machinery, out of gauge |
A dry container is the closed, general-purpose box that makes up most of the world fleet. Sizes are detailed in 20ft container dimensions and 40ft high cube container.
A reefer has a refrigeration unit and insulated walls, so its interior is smaller. Cargo must never be loaded above the red load line. See the reefer container guide.
An open top has a removable tarpaulin roof for cargo lifted in by crane or taller than the door. See the open top container guide.
A flat rack has only a floor and end walls, for machinery and out-of-gauge cargo. In ISO 6346, P1 is a platform with fixed complete ends and P3 has folding ends, so collapsible flat racks are often coded 22P3 or 45P3. Always check the code and CSC plate of the actual unit. See the flat rack container guide.
A tank container is a tank inside a container-sized frame for liquids, gases or powders; its type codes start with the letter T. Less common types include ventilated containers, bulk containers and insulated boxes without a refrigeration machine.
Reading an ISO 6346 container number
A container number has 11 characters, for example CSQU 305438 3:
| Part | Example | Meaning |
|---|---|---|
| Owner code | CSQ | Three letters registered with the BIC |
| Equipment category | U | U = freight container, J = detachable equipment, Z = trailer/chassis |
| Serial number | 305438 | Six digits assigned by the owner |
| Check digit | 3 | Control digit that catches transcription errors |
The governing standard is ISO 6346 (2022 edition), which also covers size-type codes and operational markings. Owner codes are registered by the BIC so they are unique worldwide. On the box itself, the check digit is usually printed inside a small square next to the serial number.
Other markings on the box
Besides the number and size-type code, the doors carry operational markings: maximum gross mass (MAX GROSS), tare, payload or NET, and often the cubic capacity. High cubes usually carry a height warning mark, and some boxes have an overhead power-line warning. The doors also hold the CSC plate required by the 1972 CSC Convention, which states the approved maximum gross mass, the allowable stacking load, the racking test value and the periodic examination scheme (PES) or continuous examination programme (ACEP).
When you collect an empty from the depot, match the physical number against the booking and the equipment interchange paperwork, check the seal and doors, and photograph the markings. If the number on the unit does not match the documents, stop stuffing and ask the carrier or forwarder to confirm.
How to calculate the check digit
The check digit is derived from the first 10 characters:
- Convert each letter to a number: 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. Multiples of 11 (11, 22, 33) are skipped.
- Multiply each character's value by 2 raised to its position, from position 0 for the first character up to position 9.
- Add up all the products.
- Divide the total by 11 and take the remainder. That remainder is the check digit; a remainder of 10 becomes 0.
Worked example: CSQU 305438
| Position | Character | Value | Multiplier (2^position) | Product |
|---|---|---|---|---|
| 0 | C | 13 | 1 | 13 |
| 1 | S | 30 | 2 | 60 |
| 2 | Q | 28 | 4 | 112 |
| 3 | U | 32 | 8 | 256 |
| 4 | 3 | 3 | 16 | 48 |
| 5 | 0 | 0 | 32 | 0 |
| 6 | 5 | 5 | 64 | 320 |
| 7 | 4 | 4 | 128 | 512 |
| 8 | 3 | 3 | 256 | 768 |
| 9 | 8 | 8 | 512 | 4,096 |
The total is 6,185. Then 6,185 ÷ 11 = 562 remainder 3 (562 × 11 = 6,182). The check digit is therefore 3 and the full number is CSQU 305438 3. You do not need to do this by hand every time: paste any number into the Container Number Validator.
The check digit catches any single wrong character and most swapped pairs. That matters because the container number appears on the bill of lading, the VGM, the packing list, customs filings and terminal gate data. One wrong character can leave a box stuck at the gate.
Size-type codes
A size-type code has four characters:
- First character, length: 2 = 20 ft, 4 = 40 ft, L = 45 ft.
- Second character, height and width: 2 = 8'6" high, 5 = 9'6" high (high cube).
- Last two characters, type: G1 = general purpose with passive vents, R1 = mechanically refrigerated, U1 = open top, P1 or P3 = platform/flat rack.
| Code | Meaning |
|---|---|
| 22G1 | 20 ft, 8'6", general purpose |
| 42G1 | 40 ft, 8'6", general purpose |
| 45G1 | 40 ft, 9'6" high cube, general purpose |
| L5G1 | 45 ft, 9'6" high cube, general purpose |
| 22R1 | 20 ft, 8'6", reefer |
| 45R1 | 40 ft, 9'6", reefer high cube |
| 22U1 / 42U1 | 20 ft / 40 ft, open top |
In everyday conversation people say 20GP, 40HC or 40HQ. Carrier documents and terminal systems generally use the ISO code. The ISO Type Code Decoder translates any code you do not recognise.
Common mistakes
- Mixing up the letter O and the digit 0. Letters appear only in the first four characters; the six serial digits and the check digit are always numbers.
- Dropping the check digit. A number without its last digit is incomplete and systems often reject it.
- Thinking 40HQ and 45G1 are different boxes. Both normally refer to a 40ft high cube; the 45-footer is L5G1.
- Reading weight from the type code. The code says nothing about payload; check the door markings and the CSC plate.
- Treating all flat racks as identical. P1 and P3 units are built differently; inspect the actual box.
Next steps
Validate a container number with the Container Number Validator, look up dimensions in Container Sizes, and then build your load in the 3D load planner to pick the most efficient container type.