ISO 668 · ISO 6346 · CSC
ISO Container Standards
Two standards make global container shipping interchangeable. ISO 668 fixes external dimensions and gross ratings — that is why every box is 2.438 m wide and stacks on any ship. ISO 6346 defines the identification system: the owner code, serial number and size/type code stencilled on every container.
Reading a container number
A marking like MSKU 307703 0 / 45G1 decodes as: three-letter owner code plus category letter U (MSKU — Maersk), six-digit serial, a check digit, then the size/type code. In “45G1”: the first character is length (4 = 40 ft, 2 = 20 ft, L = 45 ft), the second is height (2 = 8′6″, 5 = 9′6″), and the last two are the type (G1 = general purpose, R1 = reefer, U1 = open top, P1 = flat rack, T = tank).
| Position | Character | Meaning |
|---|---|---|
| 1st (length) | 1 | 10 ft |
| 2 | 20 ft | |
| 4 | 40 ft | |
| L | 45 ft | |
| 2nd (height) | 2 | 8′6″ standard |
| 5 | 9′6″ high cube | |
| 3rd–4th (type) | G1 | General purpose (dry) |
| R1 | Reefer | |
| U1 | Open top | |
| P1 | Flat rack | |
| T | Tank |
ISO 668 size designations
ISO 668 assigns each size a designation: 1CC (20 ft standard), 1AA (40 ft standard), 1AAA (40 ft high cube), 1EEE (45 ft high cube). US domestic 48 ft and 53 ft units sit outside the standard entirely.
| 20 ft container | 40 ft container | 40 ft high cube container | 45 ft high cube container | |
|---|---|---|---|---|
| ISO type code | 22G1 | 42G1 | 45G1 | L5G1 |
| External dimensions — Length | 6.058 m19′11″ | 12.192 m40′ | 12.192 m40′ | 13.716 m45′ |
| External dimensions — Width | 2.438 m8′ | 2.438 m8′ | 2.438 m8′ | 2.438 m8′ |
| External dimensions — Height | 2.591 m8′6″ | 2.591 m8′6″ | 2.896 m9′6″ | 2.896 m9′6″ |
| Internal dimensions — Length | 5.898 m19′4″ | 12.032 m39′6″ | 12.032 m39′6″ | 13.556 m44′6″ |
| Internal dimensions — Width | 2.352 m7′9″ | 2.352 m7′9″ | 2.352 m7′9″ | 2.352 m7′9″ |
| Internal dimensions — Height | 2.393 m7′10″ | 2.393 m7′10″ | 2.698 m8′10″ | 2.698 m8′10″ |
| Tare weight | 2,230 kg4,916 lb | 3,740 kg8,245 lb | 3,900 kg8,598 lb | 4,800 kg10,582 lb |
| Max gross weight | 30,480 kg67,197 lb | 30,480 kg67,197 lb | 32,500 kg71,650 lb | 32,500 kg71,650 lb |
| Max payload | 28,250 kg62,281 lb | 26,740 kg58,952 lb | 28,600 kg63,052 lb | 27,700 kg61,068 lb |
| Capacity (volume) | 33.2 m³1,172 ft³ | 67.7 m³2,391 ft³ | 76.4 m³2,698 ft³ | 86.0 m³3,037 ft³ |
| EUR pallets | 11 | 25 | 25 | 27 |
| TEU | 1 | 2 | 2 | 2.25 |
The CSC plate
The Container Safety Convention plate riveted to the left door is the container’s passport: max gross, tare, stacking and racking test values, plus inspection dates (ACEP or next examination date). When any figure on this site disagrees with the CSC plate of your specific unit, the plate wins.
Frequently asked questions
What does 22G1 mean on a container?
2 = 20 ft long, 2 = 8′6″ tall, G1 = general purpose dry container. Likewise 45G1 is a 40 ft, 9′6″ high cube dry box.
What is ISO 668?
The international standard that classifies container sizes and specifies external dimensions and minimum gross ratings, ensuring any container fits any ship, crane and chassis worldwide.
How is the container check digit calculated?
By a weighted modulus-11 sum over the ten preceding characters: each letter maps to a numeric value, each position is weighted by a power of 2, the total modulo 11 gives the digit (10 wraps to 0). Terminals recompute it on every gate move — a mistyped container number fails instantly.