USPS Cubic Shipping: Discounts for Small, Heavy Packages

What is USPS Cubic shipping?

USPS Cubic is a commercial shipping service available through platforms like Descartes ShipRush™, which partners with USPS to offer discounted rates. This service is not available at USPS.com or post office locations.

It applies to Priority Mail and Parcel Select and rewards shippers for using the smallest possible box or poly bag to save space and reduce shipping costs.

How do I ship small, heavy items cheaply?

USPS Cubic is the most cost-effective way to ship small, heavy packages. Here’s how:

1. Use the smallest possible packaging.
2. Confirm the package weighs 20 lbs or less.
3. Measure dimensions and calculate cubic volume.
4. If it’s 0.50 cubic feet or smaller, use software like Descartes ShipRush to access USPS Cubic rates.
5. Print your label and drop off or schedule a pickup with USPS.

What is USPS Cubic pricing?

USPS Cubic pricing is based on package size and distance, not weight. USPS Connect Ecommerce partners negotiate discounted rates—often up to 89% off retail. The heavier the package (within limits), the greater the savings. For example, packages in Zone 4 weighing 4–10 lbs may save 47–64%.

Here are some examples of shipping discounts with USPS cubic rates for Descartes ShipRush:

*Descartes ShipRush still provides shipping discounts off retail rates even if packages do not qualify for cubic rate shipping.
Pricing based on rates available May 29, 2025.

When can I use USPS Cubic shipping?

Use USPS Cubic for any domestic shipment under 20 lbs and 0.50 cubic feet (or 36” for a poly bag). It’s ideal for small, dense items—think “shipping a brick.”

Which package dimensions can I use for USPS Cubic?

Common sizes include:

• 6” x 4” x 4”
• 8” x 6” x 4”
• 12” x 6” x 4”

Packages may be up to 18” on one side, as long as total volume stays under 0.50 cubic feet.

How do I calculate cubic package volume?

• For boxes: (L × W × H) ÷ 1,728 = cubic feet
• For poly bags: Length + Width = cubic inches

How can I get USPS Cubic rates?

USPS Cubic is only available through USPS Connect Ecommerce partners. Descartes ShipRush is one such partner. Sign up, create a USPS account, and start accessing discounted shipping options, including Cubic.

How do I access USPS Cubic with Descartes ShipRush?

1. Sign up for a Descartes ShipRush account
2. Connect your ecommerce store.
3. Create a USPS carrier account to access commercial rates.
4. USPS Cubic will appear as a shipping option during label generation.
5. Set automation rules to apply USPS Cubic for qualifying shipments.

Our platform will automatically recommend USPS Cubic when it’s the most cost-effective shipping service for your package.