USPS cubic tier calculator
Priority Mail & Ground Advantage

Enter your package and see its Priority Mail Cubic and Ground Advantage Cubic tier, worked out the way USPS does it — and how much to trim to drop a tier.

Rules verified 22 Sep 2026Checked against the official rules: USPS DMM 223 (Priority Mail: DIM weight, cubic, nonstandard fees) · USPS DMM 283 (Ground Advantage — Commercial, cubic) · USPS Notice 123 — Price List. Carriers change these rules, usually each January and July — see what changed and when, and confirm against your own rate sheet or account.
Package type
Package size

Fractions are fine: 6 3/8. USPS rounds each side down to the ¼ inch.

How USPS works it out

Cubic tiers, step by step

For a box, USPS measures length, width and height at the widest points, rounds each down to the nearest ¼ inch, multiplies them and divides by 1,728. The result sets the tier: up to and including 0.10 ft³ is tier 0.10, more than 0.10 up to 0.20 is tier 0.20, and so on. USPS’s own example: 6 1/8 × 5 7/8 × 6 3/8 in rounds to 6 × 5 3/4 × 6 1/4 in = 215.6 in³ = 0.125 ft³, which is tier 0.20.

Soft packs and padded envelopes use length + width instead (each rounded down to the ¼ inch): up to 21 in is tier 0.10, over 21 up to 27 in is 0.20, over 27 up to 31 in is 0.30, over 31 up to 34 in is 0.40 and over 34 up to 36 in is 0.50.

ProgramLargest tierMax weightLongest sideRule
Priority Mail Cubic0.50 ft³20 lb22 inDMM 223 §1.3
USPS Ground Advantage Cubic1.00 ft³20 lb22 inDMM 283 §1.3

Rules verified 22 Sep 2026 · sources: USPS DMM 223 (Priority Mail: DIM weight, cubic, nonstandard fees) · USPS DMM 283 (Ground Advantage — Commercial, cubic)

Cubic is a commercial price: you get it through PC Postage or shipping software, a permit imprint account or USPS Returns — not at the Post Office counter. Soft packs top out at tier 0.50 in both programs. Compare the cubic price with the regular weight-based price for your zone before choosing.

FAQ

Questions

How is the USPS cubic tier calculated?
Measure length, width and height in inches, round each down to the nearest 1/4 inch, multiply and divide by 1,728. The tier is the next 0.1 cubic foot at or above the result: 0.125 cubic foot is tier 0.20. Soft packs use length plus width instead.
What is the maximum size for Priority Mail Cubic?
0.50 cubic foot, 20 lb, and no side longer than 22 inches (USPS DMM 223 §1.3.1). Soft packs and padded envelopes can be up to 36 inches in length plus width.
Does USPS Ground Advantage have cubic pricing?
Yes, for commercial customers: up to 1 cubic foot in 0.1 steps (0.10 to 1.00), up to 20 lb, longest side 22 inches or less (USPS DMM 283 §1.3.1).
Is cubic pricing always cheaper?
No. Cubic prices depend on tier and zone, not weight, so they usually win for small, heavy parcels. For a large, light parcel the weight-based price can be lower. Compare both in your shipping software.