What are USPS Cubic Rates?

While official USPS Cubic Pricing is available to customers that ship over 50,000 packages a year, we offer a version of that Cubic pricing to all ShipStation users through our relationship with Stamps.com. Our Cubic rates aren't as low as the official USPS Cubic Pricing, but the discount is still significant, and we don't have any minimum shipment requirement. (If you do ship over 50,000 packages a year, reach out to Stamps.com's Shipping Solutions team to see if you qualify for official USPS Cubic Rates. Once you complete the application process, we can find a way to make those super-low cubic rates available within ShipStation.​)

Cubic rates are ideal for small, heavy packages since the pricing is based on the volume of the package instead of the weight. Any package that measures 0.50 cubic feet or less and is 20 pounds or less is eligible.

Here is how the cubic measurement is calculated:

Cubic Feet = Length x Width x Height / 1728

Also note that the length, width, and height measurements should be rounded down to the nearest 0.25 inch. Here’s an example for a package that measures 6-1/8″ × 5-7/8″ × 6-3/8":

6 × 5.75 × 6.25 / 1728 = .125 cubic feet

There are 5 tiers for cubic pricing:

Tier 1 – mailpieces measuring up to .10 cubic foot
Tier 2 – mailpieces measuring more than .10 up to .20 cubic foot
Tier 3 – mailpieces measuring more than .20 up to .30 cubic foot
Tier 4 – mailpieces measuring more than .30 up to .40 cubic foot
Tier 5 – mailpieces measuring more than .40 up to .50 cubic foot

So our example above would fall into Tier 2. Let’s say this package weighs 4 pounds and is a zone 7 shipment. This would typically cost $14.69 via Priority Mail. However, the cubic price for this package is significantly lower at $7.53.

It's easy to determine the Cubic rate with Stamps.com by using ShipStation's In-App Rate Calculator.

Whether you're using the calculator or creating a shipping label, simply choose a domestic Priority service, the “Package” package type, enter the package's weight & dimensions, and then ShipStation will use the Cubic rate whenever it's cheaper than the Priority rate! Our special Cubic rates are subject to change, so reach out to our support team if you'd like a full breakdown.

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