Can you mail a watch with tritium or radium lume?

Ask this on a watch forum and you get two answers. One says just ship it, it's exempt. The other says radium can't be mailed at all. Neither cites the postal rule. Each is right for one kind of watch and wrong for the other. Below: the definition that decides it, three watches walked through the rules, the packing steps for radium, and why mail abroad is the real wall.

First, the terms the answer turns on. Lume is the glowing material on a watch's hands and markers. Old lume glowed because it held a radioactive element: radium first, then tritium, as our guide to watch lume explains.

Radioactive material, in US shipping law, is not anything that contains radioactivity. It is a legal class with a floor. The Department of Transportation defines it in 49 CFR 173.403 as "any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed" the values in the table at 173.436. A consignment is everything one sender ships at one time. Below either value, the parcel is not Class 7, the hazard class for radioactive goods. USPS uses the same definition, word for word, in Publication 52, section 347.1.

An excepted package is a Class 7 parcel so weak that most hazmat rules are lifted. It needs no warning label and no special container. A watch goes in the class for "radioactive instrument or article", which 173.403 defines as "any manufactured instrument or article such as an instrument, clock, electronic tube or apparatus". Its UN number is UN2911.

The line that decides it

PHMSA, the agency that writes these rules, put it plainly in letter 18-0088 of 15 February 2019. Is a consignment under both 173.436 values Class 7? "The answer is no." The radioactive rules apply "only to those materials meeting the definition". In letter 11-0038 it said such a parcel "is not subject to the HMR", the federal hazardous materials rules. These are the values for the three lume elements, beside the most a US watch may hold under 10 CFR 30.15:

The radium line is tiny. A 2012 study by Gillmore, Crockett and colleagues put 18 radium wristwatches at 0.46 to 32.38 kBq each, and 15 pocket watches at 2.31 to 39.31 kBq. Some sat under 10 kBq. Nobody can tell which without a laboratory reading, so our ruling is to treat every radium watch as Class 7. Our answer on whether a radium dial watch is dangerous covers those measurements.

The tritium line is the opposite. SWISS T<25 means under 25 mCi and T SWISS MADE T under 7.5, as our answer on what the T marks mean shows. Both are under 27 mCi before any decay, and a vintage dial has lost most of its tritium since. Promethium, the third lume element, is under its line too: the US cap of 100 µCi per watch is well inside 270.

A worked example: three watches, one seller

Take a seller in Ohio with three watches to post to US buyers. Here is how each goes through the rules.

1. A 1990 diver's watch marked SWISS T<25. Suppose its dial was filled to the 25 mCi ceiling. At a 12.3 year half-life, about 13 percent is left in 2026, roughly 3.3 mCi, or 122 MBq. That is about an eighth of the 1 GBq line. It is not radioactive material in law. It can go by Priority Mail like any watch.
2. A new field watch with gas tubes, rated T100. The maker NITE says T25 "contains up to 25 millicuries", under the line, while T100 "ranges from 25-100 millicuries of tritium gas". Up to 100 mCi is 3.7 GBq, nearly four times the line. Unless the maker states a figure under 27 mCi, treat it as Class 7. It goes as a UN2911 excepted package, by ground.
3. A 1944 military wristwatch with radium numerals. It has never been measured, so treat it as Class 7. Its radium is far under the cap for one article, as worked below. What decides the packing is the radiation outside the box.

Now suppose all three go in one box. The T100 and the radium watch make it Class 7, so the whole box goes by ground as UN2911. Splitting it into parcels mailed the same day may not help: in letter 13-0080 PHMSA ruled that products from one sender "on the same conveyance, at the same time" are one consignment. The same rule catches a dealer's box of tritium dials once their total passes 1 GBq.

The rule for each kind of watch

The broken radium row is our reading of two rules. The exception in 173.424 holds only if "the active material is completely enclosed by non-active components", and loose paint is not. Without the exception the parcel would need a warning label, and Pub 52 section 347.22 makes any parcel "bearing, or required to bear" one nonmailable.

How to mail a radium watch inside the US

Packaging Instruction 7A in Pub 52 sets out the steps for "instruments and manufactured articles (including clocks...)". In order:

1. Check the watch is intact: crystal in place, no loose paint, case closed.
2. Cushion it against "shock and pressure changes", inside "a strong outer packaging".
3. Use a box, not a padded envelope. At least one outside dimension must be 10 cm (4 inches) or more, and the surface limit below makes distance matter.
4. Mark the inner wrap "Radioactive".
5. Mark the address side. It must carry, in full: "This package conforms to the conditions and limitations specified in 49 CFR § 173.424 for radioactive material, excepted package–instruments or articles, UN2911 and is within Postal Service activity limits for mailing." Use a complete return address.
6. Send it by ground. Pub 52 section 327.12 lists radioactive materials as "always prohibited on air transportation", and anything sent as Priority Mail or Priority Mail Express must qualify for air. USPS calls Ground Advantage its "primary option for sending hazardous materials (HAZMAT) that can't go by air".

Two limits sit behind those steps. Unpacked, the watch must read no more than 0.1 mSv (100 µSv) per hour at 10 cm, under 173.424(d). The 2012 study's strongest wristwatch read 20 µSv per hour at 2 cm, and its strongest pocket watch 30. Both are under the limit even at that closer range. Packed, the box must read no more than 0.5 millirem (5 µSv) per hour at any point on its surface. That one can bite. A watch pressed against the side of a small mailer is about 2 cm from the outside, where the strongest watches read four to six times the limit.

Distance is the fix. Treat the watch as a point source and its dose rate falls with the square of the distance. Centered in a box 8 inches (20 cm) on each side, it sits 10 cm from every face. That cuts a 20 µSv reading at 2 cm to about 0.8, our arithmetic. This is an estimate, not a reading. A survey meter held against the packed box is the only real check.

Two more rules stay with you. Section 173.422 keeps the hazmat training rules of 49 CFR Part 172, subpart H, for excepted packages. And in 18-0088 PHMSA says "it is the shipper's responsibility to classify a hazardous material."

Why the activity limits never stop a watch

Pub 52's Exhibit 347.23 and Table 4 of 49 CFR 173.425 cap the activity in each article and each parcel. For watches, each cap is a fraction of A2, a reference amount set for every radionuclide in 173.435. Here they are, worked through by us against the two US watch limits:

The per-watch cap is the smaller number and the per-parcel cap the larger. A footnote says the tritium row also applies "to tritium in activated luminous paint". For radium we used the row for solids in "normal form". Our reading is that paint is not "special form", which 173.403 limits to a single solid piece or sealed capsule that passes the tests in 173.469.

Even the highest radium figure the 2012 paper cites, 4.5 µCi, is far inside 810. So when a radium watch fails, it fails on the surface reading or on the mail class, never on activity.

Mailing one abroad

Pub 52 section 622.3 says Class 7 materials "are permitted in international mail". Then it sets conditions a private seller will rarely meet:

• The country must accept it. Radioactive mail goes only to countries listed as accepting it in the International Mail Manual's country listings.
• Both ends need approval. "The sender and recipient of each radioactive materials shipment must receive prior authorization from the appropriate regulatory authorities within their countries."
• It must meet IAEA rules, the International Atomic Energy Agency's transport regulations, and one tenth of the domestic activity caps.
• Labels and service. A white label reading "Matières Radioactives", two endorsements and shipping papers. IMM 135.5 allows Priority Mail Express International, Priority Mail International or First-Class Package International Service.

Anything "bearing or required to bear" a White-I, Yellow-II or Yellow-III label is barred outright under section 347.21. A watch in an excepted package needs none of those labels, so the ban is not what stops it. The prior authorization is.

A single tritium paint watch is a different matter. Under the definition USPS itself uses, it is not radioactive material, so section 622.3 does not reach it. PHMSA's letter 13-0060, on tritium timepieces, adds that under the IAEA rules "Timepieces are excluded only after their sale to a consumer." The destination's own customs and radiation rules still apply. Buying from abroad? Our answer on duty on a watch bought abroad covers the tax side.

Why both forum answers persist

"It's exempt" is the right idea in the wrong law. The exemption collectors know is 10 CFR 30.15. It lets anyone who "receives, possesses, uses, transfers, owns, or acquires" a watch within its limits do so without a license. That is a Nuclear Regulatory Commission rule about owning a watch, not about how a parcel travels. For one tritium paint watch the transport rules land in the same place, through 173.436. For radium they do not: a watch at the 30.15 limit of 1 µCi is 3.7 times over the transport line.

"Radium can't be mailed" comes from the air ban and the rules abroad. Abroad, prior authorization in both countries makes it close to true. Within the US by ground it is wrong: Pub 52 names "clocks" among the items it allows.

Ground only is a cost a seller can plan for. USPS Ground Advantage includes $100 of insurance and sells up to $5,000 more "for merchandise"; our answer on insuring a watch covers whether that is enough. Buyers on eBay and elsewhere should expect a radium piece to take longer, and the vintage buying guide covers what to ask before paying. Our guide to selling a watch covers the rest of a sale.

When this answer stops applying

This page covers USPS and the federal transport rules it follows, read on 4 November 2026. It does not cover UPS, FedEx, DHL or Royal Mail: their pages did not load for us, and private carriers set their own hazmat terms. It does not cover a watch worn or packed by an air passenger, which falls under rules we did not read. The radium packing figures are estimates from published readings. Your watch may read higher, and only a meter on the packed box settles it. A seller who mails radium watches often should take the training rule in 173.422 to a hazmat trainer or the regulator, not a forum. Abroad, the destination country's rules are its own. And do not mail a damaged radium watch at all until a radiation control office has told you how to handle it.