Density decides everything
Cubic rewards weight crammed into small volume. Books, hardware, tools, and canned goods thrive under it; pillows and lampshades should not bother applying.
Priced by the cubic foot
USPS cubic pricing, from the rulebook to the rate card
Cubic pricing rates a parcel by the space it occupies instead of the pounds it weighs, which quietly rewards small, dense boxes. The rules here come from the Domestic Mail Manual and the prices from USPS Notice 123, both checked 2026-07-27, and the last section explains plainly how our own live quotes do and do not reflect these tiers.
DMM rules, citedNotice 123 tier pricesRelationship to live quotes stated
Small box, big leverage
Under cubic rating, a brick-heavy quarter-cubic-foot box can ride for single-digit dollars. The eligibility rules are the gatekeeper.
Who qualifies, per DMM section 223, checked 2026-07-27
Cubic is a commercial rating with hard edges. Per pe.usps.com/text/dmm300/223.htm: each piece must measure 0.50 cubic foot or less, weigh 20 pounds or less, and keep its longest dimension at 22 inches or under. You round each measurement down to the nearest quarter inch, then compute length times width times height divided by 1728 to get cubic feet. Soft packs rate differently, using length plus width with a combined cap of 36 inches.
One structural detail surprises people: in the current Notice 123, the cubic tables sit under USPS Ground Advantage commercial parcels, and there is no separate Priority Mail cubic table. Cubic today is effectively a Ground Advantage commercial program.
Tier prices from Notice 123, effective 2026-07-12
Five volume tiers, priced by zone. The table shows the nearest zones and the far end so the spread is visible; intermediate zones fall between them.
| Up to (cubic ft) | Zone 1 | Zone 2 | Zone 8 |
|---|---|---|---|
| 0.10 | $7.45 | $7.51 | $10.13 |
| 0.20 | $7.82 | $7.89 | $11.84 |
| 0.30 | $8.39 | $8.45 | $14.67 |
| 0.40 | $9.07 | $9.13 | $17.29 |
| 0.50 | $9.59 | $9.66 | $18.90 |
The economics jump out at the heavy end. A 20 lb brick of a box in the smallest tier rides for under eight dollars nearby, a price no weight-based rating would touch. Light, bulky parcels gain nothing; cubic exists precisely for shippers whose products are dense.
How our live quotes relate to these tiers
Straight answer: the prices in our checkout are commercial rates quoted per shipment, and they are not labeled as cubic tiers. In the 2026-07-27 capture, USPS Ground Advantage priced a 1 lb box at $9.91 from Newark to Atlanta, a 2 lb box at $8.48 on the same lane, and $11.12 for 1 lb from Los Angeles to New York. Those figures sit in the same neighborhood as the cubic table for comparable volumes, but we won't claim a tier match we can't verify from the quote itself. Use the Notice 123 grid as the reference for what a qualifying dense box can achieve, then let a live quote tell you what your actual shipment costs today.
Round down, then divide by 1728
The DMM's measurement recipe is generous in your favor: each dimension drops to the nearest quarter inch before the multiplication. At tier boundaries that rounding sometimes pays for itself many times over.
The 22 inch rule catches long boxes
A parcel can be comfortably under half a cubic foot and still flunk eligibility on its longest side. Check the single-dimension cap before celebrating the volume math.
Cubic pricing, clarified
What is USPS cubic pricing?
A commercial rating that prices a parcel by occupied volume instead of weight. In the current Notice 123, retrieved 2026-07-27, the cubic tables live under USPS Ground Advantage commercial parcels, spanning five tiers from 0.10 to 0.50 cubic feet, priced by zone.
Who qualifies for USPS cubic rates?
Commercial shippers whose parcels measure 0.50 cubic foot or less, weigh 20 pounds or less, and keep every side at 22 inches or under, per DMM section 223, checked 2026-07-27. Soft packs qualify by length plus width, capped at a combined 36 inches.
How do I calculate cubic feet for USPS?
Round each outside dimension down to the nearest quarter inch, multiply length by width by height in inches, and divide by 1728, per the DMM. The result assigns your tier: at or below 0.10, 0.20, 0.30, 0.40, or 0.50 cubic feet.
Are SMKlog's live quotes cubic prices?
They are commercial rates quoted per shipment, without a cubic-tier label we can verify, so we don't claim one. Our 2026-07-27 capture priced a 1 lb Ground Advantage box at $9.91 eastbound, close to cubic territory; the honest move is comparing your live quote against the published grid.