How to read container markings: number, size and weight (ISO 6346)
The door of every sea container carries a whole set of markings: the number, the size and type code, weight plates and safety signs. Reading them lets you verify the container by its number, know its capacity and stay within the weight limit. We break down container markings under the ISO 6346 standard — with delivery to Ukraine in mind.
What is written on a container door
The key markings:
- owner logo (the line — e.g. MSC);
- container number and check digit;
- size and type code (e.g. 22G1);
- weights: max gross, tare, payload, volume;
- plates: CSC (safety), the maker's plate;
- signs and warnings, including “High Cube” for tall containers.
The container number (ISO 6346)
The number is 4 letters + 7 digits, e.g. MSCU 123456 7:
- MSC — owner code (3 letters, registered with the BIC);
- U — category (U — freight container, J — detachable equipment, Z — chassis/trailer);
- 123456 — serial number (6 digits);
- 7 — check digit.
The check digit
The last digit is not random: it is computed from the letters and digits of the number (a modulo-11 algorithm) and serves to verify that the number was entered correctly. If the check digit does not match, the number has an error. Line and terminal systems use it to validate the container automatically.
Size and type code (22G1)
Four characters describe the container:
- 1st — length: 2 = 20 ft, 4 = 40 ft, L = 45 ft;
- 2nd — height and width: 2 = 8′6″ (standard), 5 = 9′6″ (High Cube);
- 3rd–4th — type: G1 — general purpose, R — reefer, U — open top, P — platform (flat rack), T — tank.
Example: 22G1 = a 20-foot standard general-purpose container. For more on types and sizes, see container types.
Weights
The door shows the key weights (typical values for a 20′ GP — each container has its own, stamped on the plate):
| Value | What it is | Example (20′ GP) |
|---|---|---|
| Max Gross | max gross mass (container + cargo) | 30,480 kg |
| Tare | weight of the empty container | 2,130 kg |
| Payload / Net | max cargo weight | 28,350 kg |
| Cu. Cap. | internal volume | 33.2 m³ |
Note: since 2016 the actual cargo weight is confirmed by a VGM (Verified Gross Mass) declaration under SOLAS — without it the box is not loaded onto the ship.
Plates and signs
- CSC (Safety Approval Plate) — compliance with the Convention for Safe Containers;
- The maker's plate — manufacturer and production date;
- Warning signs — “Super Heavy”, electrical safety, etc.;
- “9′6″ High Cube” — a tall-container mark (matters for clearance under bridges and tunnels).
Why it matters for an importer
By the container number you track the cargo on the line's and terminal's site, check the box on receipt, and by the weights you stay within the payload and correctly prepare the documents and the VGM. All of it is part of control on the multimodal route via the Middle Corridor.
Development prospects
Markings are going digital: QR codes and RFID/IoT sensors are added to the number, along with electronic CSC plates and real-time tracking by number with telemetry (temperature, shocks, door opening). For delivery along the Middle Corridor this means more transparent control of the container all the way.
Summary
A container's markings are its “passport”: number, size, type and weights. Reading them lets you control the cargo from dispatch to warehouse. ABU JORJIA arranges shipping and container control to Ukraine end-to-end — send a request.
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