USPS hazmat rules
Governed by USPS Publication 52, Hazardous, Restricted, and Perishable Mail. Services: Ground Advantage (surface) and Priority Mail Express and air-eligible services.
- Publication 52 is a mailability standard, not a carriage tariff: material that is not mailable is not mailable at any price, and there is no contract that changes it.
- Most mailable hazardous material is restricted to surface transportation only, which in practice means Ground Advantage.
- All lithium batteries are prohibited in international mail and in mail addressed to or from APO, FPO and DPO destinations.
By hazard class
| Class | Ground | Air | Position |
|---|---|---|---|
| Class 1 — Explosives | prohibited | prohibited | Explosives are non-mailable. Small-arms ammunition is mailable only between specifically authorised parties. |
| Division 2.1 — Flammable gas | restricted | prohibited | Flammable aerosols are mailable by surface only, in limited quantity, and only when the container is 1 L or less and meets the Publication 52 packaging standard. |
| Division 2.2 — Non-flammable, non-toxic gas | restricted | prohibited | Non-flammable compressed gases are mailable by surface only, within Publication 52 quantity limits. |
| Division 2.3 — Toxic gas | prohibited | prohibited | Toxic gases are non-mailable. |
| Class 3 — Flammable liquids | restricted | prohibited | Flammable liquids in packing group III are mailable by surface only as a limited quantity. Packing group I and II flammable liquids are non-mailable. |
| Division 4.1 — Flammable solids | restricted | prohibited | Flammable solids are mailable by surface only within Publication 52 limits. |
| Division 4.2 — Spontaneously combustible | prohibited | prohibited | Spontaneously combustible material is non-mailable. |
| Division 4.3 — Dangerous when wet | prohibited | prohibited | Dangerous-when-wet material is non-mailable. |
| Division 5.1 — Oxidizers | restricted | prohibited | Oxidizers are mailable by surface only in limited quantity. |
| Division 5.2 — Organic peroxides | prohibited | prohibited | Organic peroxides are non-mailable. |
| Division 6.1 — Toxic substances | restricted | prohibited | Packing group III toxic material may be mailable by surface; packing groups I and II are non-mailable. |
| Division 6.2 — Infectious substances | review required | prohibited | Check Publication 52 for the specific entry before mailing. |
| Class 7 — Radioactive material | prohibited | prohibited | Radioactive material is non-mailable other than a narrow set of excepted-quantity articles. |
| Class 8 — Corrosives | restricted | prohibited | Corrosives in packing groups II and III are mailable by surface only as a limited quantity; packing group I is non-mailable. |
| Class 9 — Miscellaneous | restricted | prohibited | Miscellaneous dangerous goods are generally surface-only where mailable at all. |
The three cases that catch people out
All three are Class 9, and USPS treats them differently.
| Carrier | Ground | Air | Position |
|---|---|---|---|
| USPS | prohibited | prohibited | Lithium cells and batteries sent on their own are non-mailable domestically and internationally. This is the single most common USPS hazmat violation in e-commerce. |
| USPS | restricted | prohibited | Lithium batteries installed in the equipment they operate are mailable domestically by surface only, within the Publication 52 watt-hour and lithium-content limits. Prohibited in all international mail. |
| USPS | restricted | prohibited | Dry ice is mailable domestically by surface only, marked with the net weight, and the packaging must vent. |
Carrier positions encode each carrier's published default as of the ruleset date. Tariffs change more often than regulations, and a contracted shipper may hold different terms — confirm against the carrier's current guide before the first shipment of a new item.
- Row 1: standalone lithium batteries (UN3480 and UN3090).
- Row 2: batteries in or with equipment (UN3481 and UN3091).
- Row 3: dry ice (UN1845).
Questions
- Does USPS ship hazmat?
- Publication 52 is a mailability standard, not a carriage tariff: material that is not mailable is not mailable at any price, and there is no contract that changes it. Most mailable hazardous material is restricted to surface transportation only, which in practice means Ground Advantage. All lithium batteries are prohibited in international mail and in mail addressed to or from APO, FPO and DPO destinations. Carrier positions encode each carrier's published default as of the ruleset date. Tariffs change more often than regulations, and a contracted shipper may hold different terms — confirm against the carrier's current guide before the first shipment of a new item.
- Can I ship lithium batteries with USPS?
- Standalone lithium batteries (UN3480 / UN3090): ground prohibited, air prohibited. Lithium cells and batteries sent on their own are non-mailable domestically and internationally. This is the single most common USPS hazmat violation in e-commerce. Batteries contained in or packed with equipment (UN3481 / UN3091): ground restricted, air prohibited. Lithium batteries installed in the equipment they operate are mailable domestically by surface only, within the Publication 52 watt-hour and lithium-content limits. Prohibited in all international mail.
- Can I ship dry ice with USPS?
- Ground restricted, air prohibited. Dry ice is mailable domestically by surface only, marked with the net weight, and the packaging must vent.
Check a specific SKU against USPS
The class table above is the default. Send the product itself to the API and the response carries the UN-specific rule where one exists — which is the difference between a power bank and the same cell inside a laptop.
Classify a product