USPS 13 Oz Rule (What It Means, How It Works + Other FAQs)

These days, buying postage online is fast and easy. In fact, most people probably wouldn’t even consider using postage stamps to mail a package. However, there are some people who prefer the old-fashioned way of doing things.

Unfortunately for these people, USPS has a rather strict policy concerning packages mailed with postage stamps. In this article, we’re taking a look at the 13-Ounce Mail Rule to find out what it means, why it exists, and how you can avoid it.

USPS 13 Oz Rule In [currentyear]

USPS’ 13-Ounce Mail Rule states that any mail piece weighing over 13 ounces paid for by postage stamps must be presented in-person to a USPS employee at the Post Office. This rule is USPS’ way of ensuring the safety and security of ‘anonymous mail’ (i.e. mail sent without information about the sender).

 To find out more about the 13 oz rule, including why it exists and how to get around it, make sure to read our article.

What Is USPS’ 13 Oz Rule?

USPS’ 13 oz rule, officially called the 13-Ounce Mail Rule, states that any mail piece weighing over 13 ounces that is mailed with postage stamps must be presented in-person to a USPS employee at the Post Office.

Put another way, don’t expect a package covered with stamps placed inside of a mailbox to get delivered. It won’t happen.

This rule is in place because postage stamps are untraceable and thus prone to abuse

(i.e. for sending dangerous or illegal goods through the mail). 

Therefore, USPS requires customers to present such packages in-person as a way of keeping the public, customers, USPS employees, and the mail system safe.

Upon presenting a stamp-covered package to a USPS employee, the sender will be asked about the contents of the package and where it’s headed.

While this verification process is anything but foolproof, it does serve to deter most people from using stamps as a way of abusing the mail system.

Why Did USPS Create The 13 Oz Rule?

Why Did USPS Create The 13 Oz Rule?

This rule falls under the heading of USPS’ long-standing Aviation Mail Security Rules.

Established in August 1996, these rules initially called for all packages weighing more than 16 ounces to be presented in-person to a postal clerk or letter carrier.

These rules were put in place in response to domestic terrorist Ted Kaczynski’s (better known as the Unabomber) abuse of the American mail system.

Between 1978 and 1995, Kaczynski mailed 16 bomb-containing packages through the postal service, killing 3 and wounding 23 others.

When mailing his dangerous parcels, Kaczynski would pay using only stamps (and often more than was required).

Following his capture and an investigation into his methods, USPS started requiring stamp-covered parcels to be presented in-person at a retail postal counter.

This policy has been modified several times since it was established.

For example, in 2007, USPS lowered the weight allowance from 16 ounces to 13 ounces for anonymous mail.

Then in 2019, USPS started prohibiting packages with stamps as postage that are more than ½” thick and/or weigh more than 10 ounces from entering the mail stream anonymously through collection boxes or Post Office mail slots.

While the rules have changed over the years, each modification has the goal of making the mail system as safe as possible for customers and employees.

What Happens If You Break USPS’ 13 Oz Rule?

If you break the 13-ounce rule by putting a stamped package into a collection box or dropbox, you can expect the mail piece to be returned to the sender with the postage canceled.

In fact, USPS has placed decals on their collection boxes indicating that any mail in violation of the rule will be returned to the sender.

If no sender is listed, there’s a good chance that the package will get destroyed and disposed of as a safety measure.

All things considered, it’s not a good rule to break. Not only will your package not get delivered, but you’ll also lose money on the stamps you used.

Is There A Way To Get Around USPS’ 13 Oz Rule?

Considering how strict USPS is about the 13-ounce rule, there are bound to be people looking to get around it.

Rest assured, there is, and it’s pretty simple.

If you use online shipping labels instead of postage stamps, you can send mail pieces over 13 ounces without having to make a trip to the Post Office.

In order to purchase one of these labels, you need to provide information about the sender (e.g. name and address). You’ll also likely pay with a credit card.

Entering this kind of information makes tracking the label back to you fairly simple and explains why USPS doesn’t apply the 13-ounce rule in these cases.

Shipping labels can be purchased using USPS’ online Click-N-Ship service or through an authorized USPS postage vendor.

Similarly, business customers who use postage meters may continue to use metered postage to mail packages without needing to make a trip to the Post Office.

When mailing using printed labels or metered postage, customers can deposit items in collection boxes, Post Office lobby mail slots, or give them to a letter carrier.

To know more about USPS, you can also read our posts on USPS 12 hour rule, USPS 228 labels, and USPS pay stub.


There’s a pretty good chance that you’ll never have the opportunity or need to violate USPS’ 13-ounce rule. Still, it’s a good one to know about in case you ever find yourself with a pile of stamps and a package to send out.

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Marques Thomas

Marques Thomas graduated with a MBA in 2011. Since then, Marques has worked in the retail and consumer service industry as a manager, advisor, and marketer. Marques is also the head writer and founder of

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