UN markings, field by field
The block of characters on the cage plate is the container's passport. Here is every field it contains and what each one rules in or out.
- Sheet
- 96
- Revision
- 2026-10
- Scale
- 1:1
- Drawn at
- Peoria IL
The first block: what kind of container it is
| Code | Contents | Discharge | Typical form |
|---|---|---|---|
| 11 | Solids | By gravity | Rigid box or bin |
| 13 | Solids | By gravity | Flexible bulk bag (FIBC) |
| 21 | Solids | Under pressure above 10 kPa | Rigid pressure bin |
| 31 | Liquids | n/a | The composite tote you know |
| Letters | Construction | Example |
|---|---|---|
| A | Steel | 11A |
| B | Aluminium | 11B |
| N | Metal other than steel or aluminium | 11N |
| C / D / F | Natural wood / plywood / reconstituted wood | 11C |
| G | Fibreboard | 11G |
| H | Rigid plastics | 31H1 |
| HA | Plastics inner with a steel outer casing | 31HA1 |
| HB / HC / HD | Plastics inner with aluminium / wood / plywood outer | 31HB1 |
| HG / HH | Plastics inner with fibreboard / rigid plastic outer | 31HH1 |
| HZ | Composite with an outer casing of another material | 31HZ1 |
The rest of the string
| Field | Values | Meaning |
|---|---|---|
| Packing group | X / Y / Z | X = PG I, II, III · Y = PG II, III · Z = PG III only |
| Date | MMYY | Month and year of manufacture, e.g. 0126 = January 2026 |
| Country | USA, D, NL, CA, GB… | The state that authorised the design type |
| Maker code | e.g. M5678 | Manufacturer and design type identifier |
| Stacking load | kg, sometimes a separate plate | Maximum permitted stacking load |
| Max gross mass | kg | Container plus contents |
- Leak-tightness re-test
- Every 2.5 years under US practice
- Full re-test
- Every 5 years
- Records
- Keep re-test documentation with the container serial
- If the marking is illegible
- The container is out of regulated service permanently
- After a rebottle
- Original cage marking only stands with a documented rebuild record
- After cutting
- Rating void. No exceptions, no re-certification path
Decode your own container
Type the code from your cage plate into our decoder and it will explain every field, including what it rules in and out.
Four real codes, decoded
| Code | What it is | Liquids? | Packing groups | Made | Notes |
|---|---|---|---|---|---|
| 31HA1/Y/0126/USA/M5678 | Composite IBC, plastic inner, steel cage | Yes | II and III | Jan 2026 | The classic 275/330 gallon tote |
| 31H1/Y/0324/USA/M2211 | All-plastic rigid IBC | Yes | II and III | Mar 2024 | No steel cage; different handling |
| 11A/X/0722/USA/M9043 | Steel IBC for solids | No | I, II and III | Jul 2022 | Gravity discharge, solids only |
| 31HZ1/Z/1125/D/BAM4410 | Composite, other outer material | Yes | III only | Nov 2025 | German type approval |
- The first two digits are the only field that tells you liquids versus solids. 31 means liquids; 11 and 21 mean solids, and no amount of hoping changes that.
- The packing group letter is a ceiling, not a requirement. A Y-rated container carries packing group III goods perfectly legally.
- The date is the manufacture date — not a test date and not an expiry. Re-test records are separate documents.
- Country codes you will see in the Midwest: USA, CA, D (Germany), NL, GB. The code says who approved the design type, not where the container was filled.
What to do with the marking day to day
Photograph at intake
Every container, every time, stored against the serial. Four seconds, and it has settled every marking dispute we have had since 2024.
Check before you fill
Design type against the product state, packing group against the hazard class. A five-second check that prevents an unshippable load.
Keep re-test records with the serial
Leak-tightness every 2.5 years, full re-test every 5 under US practice. A binder nobody can find is not a record.
Protect it physically
No paint, no wrap, no stickers, no close-range pressure washing, and corner boards wherever a strap crosses tube.
Does a UN marking mean the container is food grade?
No, and this is the most common misunderstanding we encounter. The marking is a transport safety certification. Food contact is a separate chain of four documents: resin certification, contents history, validated cleaning and a lab verification.
Can a reconditioner re-mark a container?
Not legitimately, if the original code is gone. The marking belongs to a tested design type and an approved manufacturer. Anybody offering to re-stamp an anonymous container is offering you an audit finding.
My container was rebottled. Is the marking still valid?
Only with a documented rebuild record showing the replacement bottle matched the design type. We keep that record against the serial and provide it on request; a rebottle with no paperwork puts the marking in doubt.
Do I need a UN-marked container for water?
No. Water is not a UN-regulated dangerous good, so for water, brine, nutrient and most general industrial duty an unmarked or illegible container is perfectly serviceable — and considerably cheaper.
What does the stacking load on the plate mean?
The maximum static load the container may carry stacked on it, measured standing still. It is not a transport rating; in transit, filled containers travel single tier.
How long is a marking good for?
Indefinitely as a certification of the design type, but the container itself needs periodic re-testing to stay in regulated service. A 2008 container with current re-test records is compliant; a 2024 container with no records is not.
Still not sure what you are looking at?
Send a photo of the plate through the form. A grader will read it and tell you what the container can and cannot legally do.