By: James McAllister


PO boxes offer a number of benefits.

Not only are they a secure place to receive mail and packages at all times, but they also act as a permanent, convenient way to receive all of your mail even if your address changes.

However, one thing that can be a little difficult when renting a PO box is determining what size of a PO box that you actually need.

USPS offers PO boxes in many different sizes, giving you a lot to choose from.

In this article, we’ll help you make that decision!

What PO Box Sizes Are Available?


USPS offers PO boxes in 5 different sizes, ranging from X-Small (3″ x 5 1/2″ x 14 3/4″) to X-Large (22 1/2″ x 12″ x 14 3/4″).

As you can see, that is quite the size difference!

But what does that actually mean in practical terms?

Let’s look briefly at each one.

1. X-Small (3″ x 5 1/2″ x 14 3/4″)

This is enough to hold 10-15 regular letters, or about the size of 2 rolled up magazines.

As you can see, USPS really does mean it when they say it’s extra small!

This PO box is only suitable for letters and the smallest of packages (like small trinkets or jewelry.) Additionally, it is best for someone that collects their mail regularly, as even those that do not receive many letters will quickly find that their PO box becomes full.

While USPS will hold mail and packages that won’t fit in your PO box for a brief period of time, it is best to purchase a PO box that will adequately hold everything that you expect to receive.

Therefore, if you aren’t ordering any packages, the X-Small size may be sufficient.

2. Small (5″ x 5 1/2″ x 14 3/4″)

Sometimes referred to as the ‘small square’ option, this one sadly isn’t a whole lot bigger.

USPS advises that is still meant to only hold 10-15 letters, though it is also large enough to hold around 5 rolled up magazines (vs. only 2 with the X-Small option.)

While there is more space meaning you could check your mail less frequently, it is still in advisable if you plan to receive packages.

3. Medium (11″ x 5 1/2” x 14 3/4″)

To paint a picture on the medium PO boxes size, it is large enough for magazines to now be able to be stacked flat.

This also means it can fit small packages, particularly if they come in poly mailers rather than boxes.

For example, clothes and other apparel may fit inside the Medium PO box.

In many post offices, this will be the largest size that is offered. Therefore, you may wish to inquire with your local post office to see if they offer any of the larger sizes on this list.

4. Large (11″ x 11″ x 14 3/4″)

Coming in at twice the size of a medium PO Box, you now have a lot of options.

With a large PO box, you should be able to safely receive most packages – including orders from marketplaces such as Amazon or Walmart.

Additionally, if you own or operate a business, customers will be able to ship returns of most products safely to this PO box.

For a frame of reference, USPS states that this size is enough to safely fit two large shoeboxes inside of the PO box, and still have room for an additional 10-15 letters.

That’s undoubtedly more than enough for most personal and business use cases!

5. X-Large (22 1/2″ x 12″ x 14 3/4″)

Finally, we have the X-Large option.

Unless you are a business or you regularly order large packages, the X-Large option is generally considered to be overkill.

It works best for businesses that have a steady stream of returns and other incoming packages that need to be received.

Coming in at over twice the size of the large option, it can easily fit over 4 large shoeboxes and several other smaller packages as well.

How To Determine What Size Of PO Box To Get

Now that we’ve looked at each size in a little bit more detail, how will you know which to choose?

Ultimately, it comes down to a few factors.

By keeping each one of these in mind, it will be easier to determine which size to go with.

1. What Will You Be Receiving?

This one seems obvious, but it’s arguably the most important detail.

What sorts of mail do you plan to have sent to your PO box?

If you plan on ordering packages for example, this likely makes the smaller sizes not very feasible. Although the post office will hold packages that don’t fit in your PO box, this is less than an ideal solution. Not to mention, you’ll have to stand in line each time you have a package you need to collect. This can lead to a lot of unnecessary time spent collecting your packages.

However, if you only tend to order things that are very small, they can still work.

Generally, the more packages you plan to order at once (and the larger you expect them to be), the larger size of PO box you should rent.

2. How Often Do You Check Your Mail?

Almost as important as the type of mail you plan to receive, you’ve got to be honest with yourself – how often will you actually check your mail?

The more frequently you check your mail, the smaller of a PO box you can get away with. This can be a good way to save some extra cash, as the price for PO boxes go up as they get larger.

Again, you need to take into account the type of mail that you will be receiving as well.

While you can go a significant amount of time without collecting your mail if you don’t order packages (even with some of the smaller sizes), if you order packages you will need to collect your mail much more frequently.

Additionally, you’ll need to be mindful of when different packages are scheduled to arrive.

While having several packages en route to your PO box usually isn’t a big deal if you check it frequently enough, there can be problems if they all arrive on the same day.

Remember, the more you check your mail, the smaller PO box you can get away with!

3. Your Use Case

Finally, you should take your intended use case into account.

Who is going to be sending you mail, and how frequently? Will you know when the mail is coming, or will it be a surprise? Are you prone to sudden surges in packages arriving?

For example, a business using a PO box for product returns may be able to settle for a large or even medium PO box the majority of the year. But what happens if their business grows? Or you throw a sale, and subsequently have lots of returns?

During Q4 when retail and online shopping surges, the quantity of returns that you receive may also skyrocket. So, this is important factor to keep in mind.

Predictability is another issue. We know PO boxes are popular for YouTubers and other influencers to keep their address private, while still being able to accept gifts from fans. However, there usually isn’t any sort of predictability with these types of packages – you may not even know that they’re arriving! So, if you don’t check your PO box very often, it can be a problem if it’s too small.

Although it’s more expensive, it’s usually best to order a larger size than you think you might need, if there’s any unpredictability in the mail that you’ll be receiving.


USPS PO boxes come in 5 different sizes, giving you a lot of options to work with.

While larger PO boxes give you a lot more room to receive larger packages and parcels, they are not really necessary for a lot of people.

I hope that you’ve found this article helpful. If you have any questions about PO boxes, please feel free to ask them using the comment form below.

Wishing you the best,

– James McAllister


About the author 

James McAllister

James is the owner of He started his first blog at the age of 11, and has since gone on to start several successful businesses. In total, these businesses have sold hundreds of thousands of units and have touched millions of lives. Here on, he shares his knowledge that brought him to where he is today. If you want to connect with James, follow him on your favorite social networks!

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