What is Priority Mail Cubic?

Learn about the most deeply-discounted USPS mail class you can only find on online shipping software
What is Priority Mail Cubic
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If you’re an eCommerce seller, saving money on shipping is absolutely critical. Shipping costs can add up over time, especially if you’re sending out lots of boxes or envelopes. Imagine saving a few bucks on every package you send out—you wouldn’t know what to do with all the extra cash in your pocket! How can you save this kind of money on shipping, you ask? Well, that’s where a specially-discounted USPS service called Priority Mail Cubic comes into play.

What is Priority Mail Cubic?

Priority Mail Cubic (or “Cubic” as we call it in the industry) is a special USPS mail class that most people have never heard of. Here’s what makes it so unique: instead of your package’s total weight determining the cost of shipping, rates are priced based on your package’s outer dimensions. As a result, shippers can load up their packages up to 20 pounds, and the cost to ship it won’t change at all! That makes Cubic the perfect USPS shipping service for sending small, heavier packages such as subscription boxes. With cubic pricing, an 18-pound package that would cost you $71.85 at the Post Office will only cost $9.65 with Priority Mail Cubic. Talk about crazy savings!

Here are the parameters your package must fall into in order to qualify for cubic rates:

  • Must weigh less than 20 pounds
  • No single dimension can exceed 18 inches
  • Total volume of your package must be less than 0.5 cubic feet
    • Find the total cubic feet by multiplying your box’s three dimensions (Length x Width x Height) and dividing that number by 1728

To see if your packages qualify for this service, check out this Smart Cubic Calculator. Feel free to play around with different combinations of dimensions to see how much you can save!

Pro Tip: You can also get Priority Mail Cubic rates by stuffing boxes into envelopes, as long as the envelopes are still small enough to qualify. This is a popular method called “box in a bag” shipping, which you can learn more about here.

You Can Only Access Priority Mail Cubic through Online Shipping Software

Here’s the kicker about Priority Mail Cubic: you’ll never find it when you walk into the Post Office. You won’t see it on USPS.com, either. You’ll only be able to ship with this special mail class when you use shipping software to buy postage online.

Online shipping software lets you access the deepest discounts that USPS typically only reserves for huge shippers sending 50,000 packages a year, or more. However, the best shipping software companies out there give you access to these special discounts for free…as well as access to ship Priority Mail Cubic. Think of using shipping software like getting invited to an exclusive restaurant that’s got the best food in town, and nowhere else even comes close!

Pro Tip: Just because a particular shipping software offers cubic rates, doesn’t mean it’s automatically the cheapest option. Most shipping software companies charge markups on top of their postage…but the best ones don’t. So, we recommend you do the research to find the cheapest rates out there.

Looking for the right shipping software for you?

To get the cheapest rates for Priority Mail Cubic, check out our guide:

Choose the Best Shipping Software

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  1. Simmie Boehm

    Can I ship old magazines to my grandchildren in the East Coast in Priority Boxes?

  2. Rickie Conley

    Paid for over night delivery, package has not been delivered. EJ306310587US


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