Box in a Bag Shipping: What You Need to Know

Putting your box in a bag is a "cheat code" that sometimes lets you save even more money when shipping USPS Priority Mail Cubic
Box in a Bag
Grab these resources for this guide
Free Shipping Software
Best USPS Discounts!
USPS Rate Calculator
Instant USPS Rate Quote!

If you’ve spent any time on our site (or on online shipping software in general), you likely know that shipping USPS Priority Mail Cubic is the best way to save money when shipping packages. However, what if we told you there was a way in which you could save even more? Well, by placing your box inside a poly mailer or envelope, you might be able to! This is a special trick known as the “box in a bag” shipping method. Lots of eCommerce shippers use this method every day to cut down their shipping costs, because when you’re shipping tons of packages, every cent counts!

What Do You Mean, Box in a Bag?

The “box in a bag” shipping method is pretty much exactly how it sounds. All you need to do is place your box inside a poly mailer, or a shipping bag. Seal the bag, buy your postage, send it off, and call me Captain Obvious!

Keep in mind that you’ll only be able to take advantage of this “cheat code” when you use online shipping software to buy discounted USPS postage online.

How Shipping Your Box in a Bag Can Save You Even More Money

We wish we had a better explanation here than “That’s just the way it is”…but this phenomenon of saving money by shipping your box in a bag is just how the math works out sometimes. Hey, we don’t make the rules! We just know how to tip the scales in our favor.

Believe it or not, shipping a box in a bag applies beyond just Priority Mail Cubic. In fact, a lot of shippers utilize the box in a bag method when sending lightweight items in smaller boxes via USPS First Class Package Service. Some examples of these kinds of parcels include shipping perfumes and fragrances.

What Cubic Pricing Tier Does My Box in a Bag Fall Into?

To calculate your cubic pricing tier, simply measure the Length and Width in inches before you put your box inside of the bag. That last part is important! USPS technically only cares about the dimensions of the empty envelope, so don’t worry about putting box inside of your bag when measuring your dimensions. If either dimension exceeds the nearest quarter inch, round down to the nearest 1/4 inch (for example, 7.8″ inches turns into 7.75″ inches).

Once you’ve got the length and width, add those together to calculate your cubic pricing tier:

  • 0.1 – Envelopes with a Length plus Width measuring more than 0″ up to 21″
  • 0.2 – Envelopes with a Length plus Width measuring more than 21″ up to 27″
  • 0.3 – Envelopes with a Length plus Width measuring more than 27″ up to 31
  • 0.4 – Envelopes with a Length plus Width measuring more than 31″ up to 34″
  • 0.5 – Envelopes with a Length plus Width measuring more than 34″ up to 36″

Once you’ve got the pricing tier that your bag belongs to, check the table below to see how much it’ll cost to ship!

Pay Attention to the Restrictions

As always, you need to be aware of certain restrictions when it comes to shipping your box in a bag. We’ve listed those out for you below.

First and foremost, neither your bag’s length or width can exceed 18″ in either direction. Also, just like regular Priority Mail Cubic, your bag’s total weight cannot exceed 20 pounds (lbs).

Last but certainly not least, you need to make sure you’re using the right kind of envelope or poly mailer. USPS will not allow you to ship the “box in a bag” method with expandable envelopes. You know the type—they’re the ones with the crease in the middle that compresses down and up to create more space inside the bag. Here’s a picture, to show you the kind of envelope we’re talking about:

Expandable Envelope

These kinds of envelopes are a no-go! If you’re using an expanding envelope like the one pictured above, USPS will treat it as a 3-dimensional box. As a result, they will charge you accordingly via their Automated Package Verification System (APV)…and no one wants that to happen.

Can I Use Any Kind of Bag? A Trash Bag Perhaps?

A lot of people wonder if they can use a trash bag to ship their box in a bag. The truth is, there’s a little bit of grey area here. USPS technically won’t restrict you from using a trash bag, but here’s what it comes down to: whatever kind of bag you use, you need to make sure it doesn’t “form fit” to the box. By “form fit,” we mean don’t tape the bag too tightly around the box. If the bag form fits to the box, then it will make the package look like a box. If it looks like a box and is shaped like a box, USPS will charge you for shipping a box. You catch our drift?

Have any questions about saving money by shipping your box in a bag? Leave a comment below!

Related Shipping Guides

One Comment

Post a Comment
  1. Lauren

    This is awesome! I was having trouble understanding the bag in a box method, and this answered all my questions! I’m excited to save even more on shipping.


Post a Comment

Your email address will not be published. Required fields are marked *


This site uses Akismet to reduce spam. Learn how your comment data is processed.