USPS Cubic Pricing: Ground Advantage Cubic vs. Priority Mail Cubic

USPS cubic pricing charges for a package by its size tier and its zone instead of its weight. Two services offer it: USPS Ground Advantage Cubic, for packages up to 1 cubic foot, and Priority Mail Cubic, for packages up to 0.50 cubic foot, both with a 20 lb weight limit (DMM 283.1.3 and DMM 223.1.3).

Cubic pays off when a product is small and heavy, and it can cost more than weight pricing when the product is light. USPS describes Ground Advantage Cubic as an option for shippers of small, heavy items.

Ground Advantage Cubic vs. Priority Mail Cubic

The size, weight and tier rules in this table come from the USPS Domestic Mail Manual, section 283.1.3 for Ground Advantage and section 223.1.3 for Priority Mail, in the versions dated July 12, 2026. The delivery times come from the USPS service pages linked below the table.

USPS lists an expected delivery time of 2–5 days for Ground Advantage and 2–3 days for Priority Mail, and the mail manual says USPS does not guarantee either (DMM 283, DMM 223).

Ground Advantage Cubic covers the wider range of box sizes. Its top tier is a full cubic foot, the volume of a 12 x 12 x 12 inch box. Past 1 cubic foot, Ground Advantage charges the greater of the actual weight or the dimensional weight, which is length x width x height divided by 139 (DMM 283.1.4). Our dimensional weight calculator runs that math for you.

Priority Mail Cubic is the faster of the two, with half the size ceiling. For more on how it works on its own, see our guide to Priority Mail Cubic.

How to find the cubic tier for a box

The steps are the same for both services (DMM 283.1.3.3, DMM 223.1.3.3):

1. Measure the length, width and height in inches at the widest point of each side.
2. Round each measurement down to the nearest 1/4 inch.
3. Multiply the three numbers and divide by 1,728 to get cubic feet.
4. Find the tier. Anything over a tier's top edge moves into the next tier up.

USPS gives this example: a box that measures 6 x 5-3/4 x 6-1/4 inches after rounding is 215.6 cubic inches, or 0.125 cubic foot. That is over 0.10, so it prices in the 0.20 tier (DMM 283.1.3.3). If you want a refresher on the volume formula itself, our cubic feet calculator guide walks through it.

Poly mailers and padded envelopes: length plus width

Soft packs (poly, plastic or cloth mailers) and padded envelopes are not priced by volume. USPS adds the outside length and width of the original mailer, rounds each down to the nearest 1/4 inch, and caps the total at 36 inches (DMM 283.1.3.4, DMM 223.1.3.4). The tiers are:

• Up to 21 inches: 0.10 tier
• Over 21 up to 27 inches: 0.20 tier
• Over 27 up to 31 inches: 0.30 tier
• Over 31 up to 34 inches: 0.40 tier
• Over 34 up to 36 inches: 0.50 tier

The same five tiers apply on both services, so a poly mailer never prices above the 0.50 tier, even on Ground Advantage (DMM 283.1.3.4). A 10 x 13 inch mailer adds up to 23 inches, which puts it in the 0.20 tier. Pleated, expandable mailers don't use this rule; USPS measures them the way it measures boxes (DMM 283.1.3.4).

When cubic saves money, and when it doesn't

The prices below are USPS commercial prices as of October 2026, from Notice 123, effective October 4, 2026. They include USPS temporary holiday prices that run until January 17, 2027, and USPS prices change again after that, so read them as an example rather than a quote.

Take a 5 lb product in an 8 x 6 x 4 inch box going to Zone 8. The box is 192 cubic inches, or 0.111 cubic foot, so it lands in the 0.20 tier. Here is what that package costs each way under Notice 123 as of October 2026:

Now put a 12 oz item in a smaller box in the 0.10 tier, also going to Zone 8. Ground Advantage Cubic costs $10.68, while the weight price for the same 12 oz package is $8.95 (Notice 123, October 2026 prices). On that package, cubic costs more.

So cubic wins when a product is heavy for the size of its box and loses when it is light. Check both prices for your own box, weight and zone before you choose. Our USPS zone map shows which zone your customers are in, and our guide to the cheapest way to ship with USPS compares the other USPS options.

How to get cubic pricing

Cubic prices are commercial prices, so you can't buy them at the Post Office counter. For Ground Advantage, they come through USPS-approved PC Postage (online shipping software that prints USPS labels), approved postage meters, or a permit imprint account (DMM 283.1.2).

For Priority Mail Cubic, USPS lists PC Postage users and permit imprint customers (DMM 223.1.3.1). Permit imprint mailings carry extra rules, including at least 200 pieces or 50 pounds per mailing (DMM 223.1.3.1), so for a small shipper, shipping software is the simpler route.

When a 3PL ships for you

If you hand fulfillment to a 3PL, buying labels and choosing carriers becomes their job. At Simpl Fulfillment, orders ship with UPS, USPS, and FedEx, and carrier selection is included in the flat per-order rate, with no carrier markup or surcharge.

Pricing starts at $7/order, and there is a $750/month minimum billed pay-the-difference. That is about 100 shipments a month when each package weighs 0.5 lb or less, and fewer when packages are heavier. If you are comparing your current postage with an all-in per-order price, our pricing page shows what is included.

Frequently asked questions

How long does Ground Advantage Cubic take?

Cubic packages travel as Ground Advantage, which USPS lists at 2–5 days. That is an expected time, not a guarantee (DMM 283).

What does “cubic” mean on a USPS label?

It means the postage was priced by the package's cubic tier and zone rather than by its weight (DMM 283.1).

What size box can I use for cubic pricing?

For Ground Advantage Cubic, up to 1 cubic foot; for Priority Mail Cubic, up to 0.50 cubic foot. On both, no side can be longer than 22 inches and the package can weigh up to 20 lb (DMM 283.1.3.1, DMM 223.1.3.1).

Can I use cubic pricing for poly mailers?

Yes. Poly mailers and padded envelopes qualify on both services. They are measured by length plus width, up to 36 inches, and top out at the 0.50 tier (DMM 283.1.3.4).