Shipping Discounts with Priority Mail Cubic

Priority Mail Cubic is the cheapest and fastest ways to send small parcels up to 20 pounds with USPS
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Have you ever heard of the term “Priority Mail Cubic?” That’s what we thought—most people haven’t! Priority Mail Cubic is one of the US Postal Service’s best kept secrets, and we’re about to let you in on it. Think of it a bit like “Animal Style” for In-N-Out Burger, except you’ll be saving tons of money on shipping packages instead of ordering secret sauce.

Table of Contents

What is Priority Mail Cubic?

We’re glad you asked! To put it simply: Priority Mail Cubic (or “Cubic” for short) is a secret service you won’t find at the Post Office, but it’s the cheapest and fastest way to ship small packages. Priority Mail Cubic isn’t priced based on weight—instead, the outer dimensions of your package determine the price. Like all Priority Mail services, Priority Mail Cubic delivery occurs between 1-3 business days, it comes with free package tracking, and even includes $100 of insurance at no extra cost. If you’re thinking that shipping Priority Mail Cubic sounds like a total no-brainer right about now, you’re absolutely correct. However, it does have some restrictions, which we’ve outlined below:

  • No one dimension on your package can exceed 18 inches
  • Total weight of your package cannot exceed 20 pounds
  • Total volume of your package must not exceed 0.5 cubic feet

If your package meets the above requirements, it’s off to the races!

Pro Tip: Priority Mail Cubic is the best for sending small, heavier items. Therefore, this is the best mail class for situations such as shipping honey and jams, shipping coffee, shipping candles and more.

How Much Does Priority Mail Cubic Cost?

Depending on the size of your package, there are five different cubic pricing tiers it will fall into. Pricing tiers are determined by cubic feet, and we’ve included those tiers in the chart below.

Cubic Feet
Up to, not over
0-150 miles
L, 1 & 2
150-300 miles
Zone 3
300-600 miles
Zone 4
600-1000 miles
Zone 5
1000-1400 miles
Zone 6
1400-1800 miles
Zone 7
1800+ miles
Zone 8
All US Territories
Zone 9

To calculate which cubic pricing tier your package falls into, follow these steps:

  1. Measure the length, width, and height of your package. When measuring your package, always round down to the nearest quarter inch. For example, if your package height is 6.3 inches, round it down to 6.25.
  2. Once you’ve got your dimensions, multiply them all together (Height x Width x Length). Next, take that number and divide it by 1728.
  3. The resulting decimal is the size of your package in cubic feet. Use the chart above to determine the pricing tier, always rounding up fractional results to the next tier (for example: if your package is 0.24 cubic feet, it will fall into the 0.3 tier).

Not in the mood to do the math? You can use this handy Priority Mail Cubic Calculator. Just type in your dimensions, and it will automatically tell you which pricing tier your package falls into. The calculator also makes suggestions to help you get the most bang for your buck on your package size!

Pro Tip: Be smart with your package dimensions! If the contents of your package allow for it, it’s a good idea to plan your package to fit within the smallest tier possible. The best part is: since Cubic pricing isn’t based on weight, you can stuff your package to the brim! Just make sure the total weight doesn’t exceed 20 pounds. Doing this can drastically lower your cost of shipping. In fact, your shipping costs will be so low that your business can offer free shipping, which is a tried and true way to build customer loyalty. Makes sense, right? Don’t worry…your secret’s safe with us.

Priority Mail Cubic in Action

Want to see how Priority Mail Cubic stacks up against the competition? Let’s try a simple exercise. Imagine you have an 8x8x8 box that weighs 10 pounds, and you’d like to ship it from Los Angeles to Denver. The distance between those cities is approximately 1,016 miles, which puts your shipping rate in Zone 6 (you can see that in the chart above). If you ship the box USPS Priority Mail with a 3-day transit time, that price at the 2020 USPS Commercial Pricing rates would come to $26.67.

Using Cubic Shipping, that same package (in the .3 cubic tier) would cost only $10.98 for Zone 6. That’s about 41% less!

Cubic also beats UPS and FedEx Ground prices by a landslide. For the same 10-pound package, FedEx Ground (4-day transit time) would cost $19.00. After applying residential delivery surcharges, the UPS rate would be similar. Applicable fuel surcharges would also apply to both UPS and FedEx, potentially pushing both costs up to $20 or $21. Considering the $10.98 rate you you can get with Priority Mail Cubic, there’s simply no comparison.

You Can Also Use Cubic for a Poly Mailer or Padded Envelope

Believe it or not, Priority Mail Cubic isn’t just for boxes! You can also use USPS Cubic for a soft-pack or padded envelope. This process is known as “box in a bag” shipping. Just like with regular boxes, you’ll need to make sure that your sides aren’t over 18 inches in each direction. Also, the total weight of the envelope can’t exceed 20 pounds.

Here’s the thing, though. You’ll need to measure the envelope’s dimensions before you put anything in it. Only measure the length and the width of the envelope (since envelopes technically don’t have a height dimension). When you add the length and width together to get the total inches, that number will determine which pricing tier your envelope belongs to. The total number of inches cannot exceed 36.

Pro Tip: You can’t use expandable or pleated envelopes! If your envelope expands, it technically has a third dimension (height), so you’ll need to measure it the same way you would a box: length + width + height.

Ready to Start Saving Money on Shipping?

In the words of the wise DJ Khaled, “They don’t want you to know about Priority Mail Cubic!” But guess what? We want you to know. Shipping Priority Mail Cubic is simply one of the cheapest ways to ship with USPS, and you can start right now. There are several shipping software options out that sell Priority Mail Cubic postage at discounted rates. However, they’re all a bit different, and some are certainly better than others. Before your start shipping, we suggest doing research to see which one best fits your needs!

Looking for the right shipping software for you?

To get the deepest discounts on all USPS shipping services, check out our guide:

Choose the Best Shipping Software

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Post a Comment
  1. Honest Abe

    Can i use one of the free priority mail boxs that are normally used fir fixed rate retail for my priority mail cubic package?

  2. Kim

    Is this the same thing as the USPS Flat Rate shipping?

    • Rockwell Sands

      Hi Kim – no, it’s not. Cubic prices aren’t the same as flat rate pricing, and fluctuate based on the size of your package, and how far it needs to travel. Flat rate, on the other hand, stays the same as long as whatever you’re shipping fits into the flat rate packaging. You can read more about that here.

  3. Juliana

    I am confused about how you actually send Priority Mail Cubic. Do you bring it to the post office and tell them that this is cubic? If your mailman picks up your boxes (I no longer drive so have to use Lyft to get to post office,) do you have to have postage on the cubic box? Is so, how do you get a postage label?

    • Rockwell Sands

      Hi Juliana – You can’t bring a package to the Post Office and ask for cubic rates. You need to buy this postage online through shipping software solutions that offer Priority Mail Cubic labels. You can check out Pirate Ship and plug in your box’s to see if your package will qualify for cubic rates: I hope this helps!

  4. Tabatha

    This shipping cubic priority only works if you have a download a program. I tried going to the post office and asking for it that is what they told me.

    • Angela Giuffrida

      No Response? Hummm
      Thank you. You have saved me a trip to the Post Office. I wanted to use this for my Poshmart packaging.

  5. Frank Lanti

    Would this work for international priority ?
    How would you generate a label with this Cubic service?

    • Rockwell Sands

      Hi Frank – Priority Mail Cubic only applies to domestic shipments that qualify! You can only get it with certain shipping software. Here’s the one I use…you can see if your package qualifies by typing its dimensions, weight, and recipient info into the rates calculator:

  6. peter

    Would this be a good option to ship small electronic items?

    • Rockwell Sands

      Peter – definitely! Cubic is a good option to ship just about anything, as long as you can legally ship it 😉

      Keep in mind that you may need to follow certain guidelines if your electronics contain lithium ion batteries. You can read more about that here:

  7. Nina

    How do I mail HEET fuel additive to myself while I hike the AT? I am using it for stove fuel. Is it considered hazardous?

  8. Polonia

    How do I designate a package for Priority Mail Cubic?

    • Rockwell Sands

      Hi Polonia – you can’t really “designate” your box for cubic, but as long as it qualifies, most shipping software options will select Priority Mail Cubic as the default service, since it’s so heavily discounted and cheaper than regular weight-based Priority Mail in most cases.

      Here are the specs your box needs to meet to qualify: 1) must be under 20 pounds; 2) No dimension can exceed 18 inches; and 3) total volume must be under 0.5 cubic feet

      Hope this is helpful! You can plug in your package info into this calculator to see if your box qualifies.

  9. Entsar

    Can I ship from Tanzania in Africa to USA

    • Rockwell Sands

      Hi Entsar – you can, but you can’t use USPS and therefore can not ship via Priority Mail Cubic. You’ll need to use a different carrier, like FedEx, if there are FedEx locations in Tanzania.

  10. Kelly

    Can you mail from the states to Canada?
    What about covid restrictions on shipping?

    • Rockwell Sands

      Hi Kelly, you can absolutely mail from the United States to Canada. However, keep in mind that Priority Mail Cubic is only a domestic service; if you need to ship internationally, you’ll be restricted to either First Class Package International, Priority Mail International, and Priority Mail Express International.

      In terms of COVID restrictions, there aren’t any that apply to shipments going to Canada at this time.


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