Priority Mail Cubic is a special version of Priority Mail that’s priced based on the outer dimensions of your package instead of the weight, which can save you up to 89% off what it would otherwise cost. Cubic is the cheapest, fastest way to ship small packages that weigh over 1 pound, with delivery in 1-3 days and $100 in insurance included for free.

You can ship packages that are up to half of a cubic foot in volume with this service (which is 12x12x6 inches, or other combinations that make the same volume) and your packages can weigh up to 20 lbs. Note that to qualify for Cubic rates, the maximum size for any dimension is 18".

Depending on the size of your package, there are 5 pricing tiers it will fall into. It’s a good idea to plan your packaging to fit within the smallest tier possible for your package’s content, because it can drastically lower your costs.

### Priority Mail Cubic Pricing Tiers

To calculate which of the 5 tiers your package will be in you can use our Priority Mail Cubic Pricing Calculator or the manual formula below:

Measure your package’s outer dimensions

If any of the measurements exceed the nearest quarter inch, round down to the nearest quarter inch (for example, 5.6 inches turns into 5.5 inches)

Multiply Length x Width x Height, and divide the result by 1728

For example, to calculate the Cubic tier for a box that is 12.3" x 9.5" x 3":

Round down to 12.25" x 9.5" x 3"

Multiply 12.25" x 9.5" x 3" = 349.125

Divide 349.125 / 1728 = .202

Because this package is just over .2 cubic feet, it would be in the 0.3 cubic feet pricing tier.

If it were a slightly smaller box (such as 12x9.5x3) it would be in the 0.2 pricing tier instead and would cost less to ship.

### You can use Priority Mail Cubic with an envelope or poly mailer

Note that you can also use a padded envelope or poly softpack, but it changes the formula used to determine your pricing tier. Learn more about Priority Mail Cubic Softpack here.

### You cannot use Priority Mail Cubic with tubes

Cubic-priced mailpieces may not be rolls or tubes.

### USPS Priority Mail Cubic rates

Once you know which USPS Cubic pricing tier your package is in, you can use Priority Mail Cubic rate chart to determine what it will cost to ship your package, or use our USPS rates calculator.

Generally speaking, Priority Mail Cubic offers the cheapest rates when shipping to Zones 1-4, and becomes more expensive when shipping to Zones 5-8. Don't worry, though; our software always displays the cheapest service option for you no matter what you're shipping, and where. Sometimes it's Cubic, and sometimes it isn't!

One final thing to remember is that the size of your box or envelope matters! The smaller your package is, the less it will be to ship it with Priority Mail Cubic.

### Pirate Ship offers true Commercial Pricing for Priority Mail Cubic

Other shipping software adds tons of markup on top of the actual Priority Mail Cubic rates. Pirate Ship is the only shipping software that passes through the deepest discounts available for Priority Mail Cubic for free, with no markup, fees, or minimum volume required.