USPS Cubic Pricing Explained: Ground Advantage Cubic and Priority Mail Cubic

USPS cubic pricing charges a package by the size of the box, not by its weight. You measure the box, work out its volume in cubic feet, and pay the price for that size tier and zone. It is only for small boxes and mailers: up to 1 cubic foot for USPS Ground Advantage Cubic, up to 0.5 cubic foot for Priority Mail Cubic, with a 20 lb limit and no side longer than 22 inches. Cubic is a way of pricing, not a different service — the package travels as normal Ground Advantage or Priority Mail. It saves the most on small, heavy items: a 5 lb item in an 8 x 6 x 4 inch box costs $9.92 with Ground Advantage Cubic to Zone 5, against $14.53 priced by weight (USPS holiday prices, October 4, 2026 to January 17, 2027).

Who can get cubic prices?

Cubic is a commercial price. You can't buy it at the Post Office counter. USPS offers it through USPS-approved PC Postage (online postage) products to their registered users, and to permit imprint mailers. For Ground Advantage, USPS-approved IBI postage meters that send data to USPS also qualify. In practice, that means an online postage service that sells USPS commercial prices.

Priority Mail permit imprint mailers have extra rules: a mailing of at least 200 pieces or 50 lbs, and an electronic manifest. That doesn't apply when you buy single labels online.

The rules

• Ground Advantage Cubic: 1 cubic foot or less, 20 lbs or less, longest side 22 inches or less (10 tiers: 0.1 to 1.0)
• Priority Mail Cubic: 0.5 cubic foot or less, 20 lbs or less, longest side 22 inches or less (5 tiers: 0.1 to 0.5)
• Rolls and tubes can't use cubic prices
• Soft packs (poly mailers) and padded envelopes are measured a different way — see below

How to work out your cubic tier

Example: an 8 x 6 x 4 inch box is 192 cubic inches. 192 ÷ 1,728 = 0.111, which is just over 0.10, so it is tier 0.2. Trim the height to 3-1/2 inches and it is 168 ÷ 1,728 = 0.097 — tier 0.1, and a cheaper price.

1. Measure the length, width and height at the widest point of each side, in inches.
2. Round each one DOWN to the nearest quarter inch. For example, 6-1/8 inches becomes 6 inches, and 5-7/8 becomes 5-3/4.
3. Multiply length x width x height, then divide by 1,728.
4. Find your tier. Each tier covers 0.1 cubic foot: up to 0.10 is tier 0.1, more than 0.10 up to 0.20 is tier 0.2, and so on.

Poly mailers and padded envelopes

For soft packs and padded envelopes, USPS uses length plus width instead of volume. Measure the flat mailer, round each side down to the nearest quarter inch, and add them. The total can't be more than 36 inches. Expandable (pleated) mailers are measured like boxes instead.

• Tier 0.1: up to 21 inches (for example, a 10 x 10 inch mailer)
• Tier 0.2: more than 21 up to 27 inches (for example, 10 x 13)
• Tier 0.3: more than 27 up to 31 inches
• Tier 0.4: more than 31 up to 34 inches
• Tier 0.5: more than 34 up to 36 inches

Ground Advantage Cubic prices (2026)

USPS holiday prices, in effect October 4, 2026 to January 17, 2027. From July 12 to October 3, 2026 each price was a little lower (for example, tier 0.2 to Zone 5 was $9.37).

• Tier 0.1: $8.39 to Zone 4 · $9.04 to Zone 5 · $10.68 to Zone 8
• Tier 0.2: $8.74 to Zone 4 · $9.92 to Zone 5 · $12.39 to Zone 8
• Tier 0.3: $9.63 to Zone 4 · $11.51 to Zone 5 · $15.22 to Zone 8
• Tier 0.5: $11.58 to Zone 4 · $14.37 to Zone 5 · $19.95 to Zone 8
• Tier 1.0: $15.59 to Zone 4 · $18.68 to Zone 5 · $27.35 to Zone 8

Priority Mail Cubic prices (2026)

USPS holiday prices, October 4, 2026 to January 17, 2027:

• Tier 0.1: $10.90 to Zone 4 · $13.87 to Zone 5 · $16.36 to Zone 8
• Tier 0.2: $11.19 to Zone 4 · $14.02 to Zone 5 · $17.22 to Zone 8
• Tier 0.3: $13.08 to Zone 4 · $17.41 to Zone 5 · $21.42 to Zone 8
• Tier 0.4: $15.77 to Zone 4 · $21.98 to Zone 5 · $29.05 to Zone 8
• Tier 0.5: $16.75 to Zone 4 · $24.06 to Zone 5 · $32.31 to Zone 8

When is cubic cheaper than paying by weight?

Cubic wins when the item is heavy for its size. It loses when the item is light. Same box, Zone 5, USPS holiday commercial prices:

• 5 lb item in an 8 x 6 x 4 box (tier 0.2): Ground Advantage $14.53 by weight vs $9.92 cubic. Priority Mail $23.27 by weight vs $14.02 cubic.
• 3 lb item in a 12 x 9 x 4 box (tier 0.3): Ground Advantage $12.12 by weight vs $11.51 cubic — a small saving.
• 8 oz item in an 8 x 6 x 4 box (tier 0.2): Ground Advantage $8.24 by weight vs $9.92 cubic — weight is cheaper.
• 10 lb item in a 12 x 12 x 12 box (tier 1.0): Ground Advantage $17.81 by weight vs $18.68 cubic — weight is cheaper.

Ground Advantage Cubic vs regular Ground Advantage

It is the same service — same network, same tracking and same delivery. Only the price is worked out differently. If your shipping label says 'Cubic', the postage was priced by the box's cubic tier instead of its weight.

Ground Advantage Cubic vs Priority Mail Cubic: Ground Advantage is cheaper and accepts bigger boxes (up to 1 cubic foot). Priority Mail is the faster service but stops at 0.5 cubic foot.

• USPS Ground Advantage: full guide →
• Ground Advantage vs Priority Mail →

Frequently asked questions

What does cubic mean on a USPS label? The postage was priced by the package's size tier, not its weight. Delivery is the same as the normal service.

What is the weight limit for USPS cubic? 20 lbs for both Ground Advantage Cubic and Priority Mail Cubic.

Can I get cubic prices at the Post Office? No. Cubic is a commercial price, sold through USPS-approved online postage products and to permit imprint mailers.

Is cubic always cheaper? No. For light items, the weight price is often lower. Compare both before you buy.

Do I round measurements up or down for cubic? Down, to the nearest quarter inch. (For dimensional weight on big boxes it's the opposite: USPS rounds up to the next whole inch.)