Packaging Technical Library › Hazmat Packaging › UN Codes · Document TL-004
Every packaging certified for hazardous materials carries a UN mark: a short code that says what the packaging is, what it was tested to hold, and who certified it. This guide is the key to that code: packaging type numbers, material letters, packing group ratings, the solids and liquids formats, and the suffix letters, with worked examples.
Example mark on a combination package. Read it as: a fiberboard box, tested for Packing Group II and III, up to 25 kg gross, for solids or inner packagings, made in 2026, certified in the USA by registrant M1234.
Reading the UN mark, field by field
| Field · example | What it means | |
|---|---|---|
| 1 | UN packaging symbolu/n | Certifies that the packaging design passed UN performance tests (drop, stacking, and for liquids, leakproofness and hydrostatic pressure). Embossed metal may show “UN” instead. |
| 2 | Packaging type4 | A number for the kind of packaging: 1 drum · 3 jerrican · 4 box · 5 bag · 6 composite. (2 is reserved; it was once used for wooden barrels.) |
| 3 | MaterialG | A letter for the material: G = fiberboard. Drums, jerricans and bags add a number for the category, e.g. 1A1 tight-head or 1A2 open-head steel drum. |
| 4 | Packing group ratingY | X = PG I, II and III · Y = PG II and III · Z = PG III only. The letter is a ceiling, not a match. |
| 5 | Gross mass or specific gravity25 | For solids and inner packagings: the maximum gross mass in kg. For single packagings of liquids, this position holds the maximum specific gravity instead, e.g. 1.4. |
| 6 | Solids, or test pressureS | S = solids or inner packagings. On a liquids mark this position holds the hydrostatic test pressure in kPa, e.g. 150. |
| 7 | Year of manufacture26 | Last two digits of the year. Plastic drums and jerricans also show the month, often as a clock-style dial. |
| 8 | Authorizing countryUSA | The country (state) that authorized the mark, by its vehicle registration code. This can differ from where the packaging was made. |
| 9 | Manufacturer / certifierM1234 | The name or registered symbol of the manufacturer or the approval agency. In the U.S., symbols are registered with PHMSA. |
Material letters
| Letter | Material |
|---|---|
A | Steel (all types and surface treatments) |
B | Aluminum |
C | Natural wood |
D | Plywood |
F | Reconstituted wood |
G | Fiberboard |
H | Plastic |
L | Textile |
M | Paper, multiwall |
N | Metal other than steel or aluminum |
P | Glass, porcelain or stoneware |
Suffix letters
| Letter | Meaning |
|---|---|
V | Special packaging tested with a range of inner packagings, e.g. 4GV |
W | Equivalent packaging approved by the competent authority |
T | Salvage packaging, for damaged or leaking packages |
Solids vs. liquids formats
Solids: 4G/Y25/S/26/… — max gross mass (kg) + “S”.
Liquids: 3H1/Y1.4/150/26/… — max specific gravity + test pressure (kPa).
Common codes
| Code | Packaging |
|---|---|
1A1 / 1A2 | Steel drum, tight head / open head |
1H1 / 1H2 | Plastic drum, tight head / open head |
3H1 | Plastic jerrican, tight head |
4G | Fiberboard box |
4H2 | Solid plastic box |
5H4 | Plastic film bag |
6HA1 | Plastic receptacle in a steel drum |
31HA1 | Composite IBC tote (see TL-003) |
Rules that trip people up
- Combination packages carry the mark on the outer packaging; the mass is for the whole package. Inner packagings are usually unmarked.
- Pack it as tested. Same inner packagings, cushioning and closures, closed per the maker’s closure instructions (49 CFR 178.2).
- Legible size. Characters at least 12 mm tall on packagings over 30 L or 30 kg, and at least 6 mm on those of 5 to 30 L.
Before you fill: a four-step check
S mark. Liquids in single packagings need a specific gravity and test pressure mark.Frequently asked questions
What do UN markings on packaging mean?
A UN mark certifies that the packaging design passed UN performance tests for hazardous materials. It gives the packaging type and material, the packing groups it may carry, its maximum gross mass (solids) or specific gravity and test pressure (liquids), the year of manufacture, the authorizing country and the manufacturer or certifier.
What does 4G mean on a box?
4G is the UN code for a fiberboard box: 4 means box and G means fiberboard. A 4GV is a fiberboard box tested as special packaging, which allows a range of inner packagings.
What is the difference between X, Y and Z?
They set the packing groups the design may carry. X covers Packing Groups I, II and III; Y covers II and III; Z covers III only.
Do inner packagings need a UN mark?
Usually not. In a combination package the UN mark goes on the outer packaging and covers the package as tested with its inner packagings.
Why does a liquids mark show 1.4/150 instead of a weight?
For single packagings of liquids, the mark gives the maximum specific gravity the design was tested at (1.4) and the hydrostatic test pressure in kPa (150) instead of a gross mass and an S.
Find suppliers of UN boxes, drums, jerricans, bags and IBCs in the Packaura directory, or send one RFQ to vetted manufacturers and distributors.
Browse suppliers Request quotesMore from the Technical Library
- UN Markings: Open-Head Steel Drums (Solids) · TL-001
- UN Markings: Tight-Head Steel Drums (Liquids) · TL-002
- IBC Tote UN Codes and Markings · TL-003
For reference only. This guide explains the marking format and does not replace the regulations or your packaging’s test report. Confirm against 49 CFR 178.502–178.503, 49 CFR 178.2 and the UN Recommendations on the Transport of Dangerous Goods, Model Regulations, Chapter 6.1. Air (IATA DGR) and sea (IMDG) add their own rules. The mark shown is an example, not a real certification.