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How to Get Cheaper Shipping Rates with USPS Priority Mail Cubic

  • Matthew Holman - SUBTA Operations Committee Co-Chair
  • Sep 9, 2021
  • 4 minute read

There is a relatively unknown shipping program that offers incredible rates for packages that are between 1 and 20 pounds. Proportionally speaking, it is one of the best shipping services out there, allowing you to send certain packages for cheaper than normal using USPS Priority Mail.

Unlike dimensional surcharges handed out by FedEx and UPS — which penalize you for heavier or larger boxes — USPS Cubic rewards you for fitting your products into a smaller box. This allows USPS to minimize empty space on its planes and trucks.

For example, shipping something as simple as a hat, bag, and decal that weighs 5.1 pounds would cost you $25 going to Zone 8 on regular USPS Priority. Putting those same items in an 8 x 8 x 8 box and using USPS Priority Cubic would only cost $13.25 — and get there in the same amount of time!

Does it sound too good to be true? Let’s break down how this service works so you can take advantage of it in your shipping program.

How USPS Priority Mail Cubic Works

As mentioned above, Cubic has a unique pricing method that doesn’t take into account the weight of your package. This works particularly well for anyone shipping anything heavy (basically not feathers) or long distance. But even something as light as a backpack or a t-shirt can do well in Cubic if you package it into a small box. 

It all comes down to size, not weight.

Here are the steps you need to take to calculate your package with Cubic:

  1. Measure the length, width, and height of your package. Round each dimension down to the nearest quarter inch. For example: 3 x 10 x 12 package
  2. Multiply the dimensions together (Height x Width x Length) and then divide that number by 1728. For example: 3 x 10 x 12 = 360 / 1728 = 0.2083
  3. The decimal you get back is the size of your package in “cubic feet.” You have to round up to .1, .2, .3, .4, or .5. For example: .2083 rounds up to .3 (see chart below for finding the cost)

Cubic pricing does not take weight into account. As long as your package is less than 20 lbs, no longer, wider or taller than 18”, and is smaller than .5 cubic feet, your shipment costs will decrease.

USPS Pricing Tiers

When it comes to cubic-feet measurement, your package will fall into one of five tiers that USPS uses to calculate the shipping rate:

  • Tier 1: Up to .10 cubic feet
  • Tier 2: More than .10 and up to .20 cubic feet
  • Tier 3: More than .20 and up to .30 cubic feet
  • Tier 4: More than .30 and up to .40 cubic feet
  • Tier 5: More than .40 and up to .50 cubic feet

2020 USPS Priority Mail Cubic Rates

How much you’ll be paying depends on your cubic dimensions and your zone. Here’s a table of what the 2020 rates for USPS Priority Mail Cubic looked like to give you an idea:

These rates aren’t posted on the USPS website because they are commercial rates. This data was provided by Essential Hub.

Benefits of USPS Priority Mail Cubic

Not everyone likes using the post office for shipments, but I’m a big fan. USPS Priority Mail Cubic pricing offers many benefits that you won’t find from other carriers — without hidden fees or compounding surcharges. These include:

  • Fast Delivery Within One to Three Business Days: The USPS Priority Mail Cubic service enables you to ship your items to customers within one to three days across all states in the USA.
  • Free Package Tracking: USPS will offer free package tracking on shipments so you can follow the journey of your product.
  • Cheapest Price for Small Packages: With Cubic, you get much more competitive rates than if you were shipping from other carriers.

Cubic offers you the possibility to save big on all of your shipping. What makes it difficult is that not every third-party shipping softwares offers this service — or true Cubic pricing.

How You Can Get Started With Priority Mail Cubic

The best way to get started with Cubic is to integrate a shipping app. However, since Cubic is a relatively unknown program, certain softwares markup the price.

Finding commercial-level pricing for Cubic can also be a difficult task, though not impossible. Popular tools like PirateShip and Shippo are able to help you, unlike others — including Shipstation.

Wrapping Things Up

There isn’t a single service out there that is the best price on all sizes across all zones for all delivery expectations. 

Finding the best rates can be a bit tricky, which is why software can be a big help. For anyone shipping something that can fit inside a box under 18 inches and 20 pounds, especially to farther zones, it’s worth checking out!


Do you want to learn more about shipping solutions in the subscription industry? Join SUBTA. We’re a community of doers, excited to share insights, make connections and grow your subscription brand.