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DimCheck

USPS Dimensional Weight Calculator

USPS applies dimensional weight only to packages over one cubic foot. Since July 12, 2026, the divisor is 139 and every dimension rounds UP to the next whole inch.

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Use a custom DIM divisor only if your shipping agreement specifies one. It applies only to this calculation — official carrier rules are never changed.

Safety allowance is a planning buffer for packaging variation, not a prediction of carrier measurement error.

Monthly shipments power the Business Impact metric (excess billable weight × volume).

The one-cubic-foot threshold

Unlike FedEx and UPS, USPS does not apply DIM weight to every package. If your rounded volume is at or below 1,728 in³ (one cubic foot), billable weight is simply the actual weight. Above 1,728 in³, DIM weight is volume ÷ 139, rounded up, and capped at the 70-lb price. The diagnosis below shows whether DIM applies to your box.

USPS-specific warnings

  • Nonstandard Length fee applies above 22 in longest side, with a higher tier above 30 in.
  • A Nonstandard Cubic Volume fee applies above 2 cu ft (3,456 in³) — only the highest length fee applies, but the volume fee can stack on top.
  • Priority Mail and Priority Mail Express are limited to 108 in length + girth; Ground Advantage and Parcel Select allow up to 130 in (with an oversized price above 108 in).
  • USPS published these rules in imperial units only; metric results here are the exact equivalents.

Worked example

A 12 × 12 × 12 in box is exactly 1,728 in³ — no DIM weight, billable is the actual weight. A 12 × 12 × 13 in box is 1,872 in³ ÷ 139 = 13.5 → 14 lb DIM weight. And a 23-in longest side triggers the Nonstandard Length fee; at 22 in you are one inch away.

Official sources

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Compare all carriers · Length + girth calculator · Box size optimizer