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.
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.
The July 2026 divisor change, in dollars-and-pounds terms
The divisor was 166 until July 12, 2026; it is 139 now, and every dimension rounds up to the next whole inch as of the same date. The same physical box now produces more DIM weight than it did a year ago: a 24 × 18 × 12 in box (5,184 in³) was 5,184 ÷ 166 = 31.2 → 32 lb and is now 5,184 ÷ 139 = 37.3 → 38 lb. For any package above the one-cubic-foot threshold that is roughly a 19% jump in the DIM side of the bill — see the USPS DIM weight guide for the full picture, including the 70-lb cap and the nonstandard fees.
Official sources
Related tools
Compare all carriers · Length + girth calculator · Box size optimizer
Frequently asked questions
Does USPS charge dimensional weight on every package?
No — USPS is the one major US carrier with a volume gate: DIM weight applies only when the rounded volume exceeds 1,728 in³ (one cubic foot). At or below that, USPS prices by actual weight alone. Above it, DIM weight is volume ÷ 139, rounded up. This is also where rounding bites: a box measured at 11.9 × 11.9 × 12.2 in is 1,727.6 in³ of real volume but rounds to 12 × 12 × 13 = 1,872 in³, which is over the threshold.
Is the USPS DIM divisor 139 or 166?
139 — since July 12, 2026. USPS used 166 before that date, and most online references and older calculators still show 166. The divisor change also came with round-up dimension rules: every side now rounds up to the next whole inch before USPS multiplies the volume. DimCheck's numbers follow the current DMM and Notice 123, verified August 30, 2026.
How does the USPS 70 lb cap work?
When a package's DIM weight would exceed 70 lb, USPS prices it at the 70-pound rate instead of the computed figure — the DIM weight is capped, not charged in full. The cap matters for big light boxes: a 40 × 30 × 30 in package computes to 259 lb of DIM weight (36,000 ÷ 139) but bills at the 70 lb tier. Actual weight over 70 lb is still over the service maximum for most USPS parcel products.