Methodology and sources
Every number on this site traces to one dataset, and every dataset entry traces to an official source with a checked date. This page explains the system.
One dataset, many tools
All calculators read the same figures: carrier divisors and rounding, the NMFC density scale, pallet footprints and container volumes. No page keeps its own copy of a divisor or a density band, so the tools cannot disagree with each other. When a figure changes, it changes once, in the dataset, and every tool and table that uses it updates together.
Where the figures come from
Parcel rules come from the carriers' own publications: the UPS Rate and Service Guide, the FedEx Service Guide, the USPS Domestic Mail Manual and the DHL service guide. Freight class comes from NMFTA disposition bulletins and the NMFC. Pallet footprints follow the ISO 6780 series, and container volumes use Maersk's published equipment specifications. Each page lists its sources at the foot, and each figure carries the date it was last checked. Rules on this site were last checked on November 12, 2026.
When figures are rechecked
Carrier rules change on a calendar, so checking follows that calendar instead of running constantly. New UPS and FedEx guides and USPS January changes are checked in late December and January. USPS mid-year changes and NMFTA summer dockets are checked in June and July. The rest of the year, NMFTA bulletins and carrier change notices get a monthly check. A change is never published on one source alone: it is confirmed against a second source, the fixed test cases below are re-run, and the change is logged before the dataset updates.
Fixed test cases
A set of fixed cases with known answers runs before any update ships. An 18 × 14 × 10 in package at 12 lb must return a DIM weight of 19 lb at divisor 139. A USPS parcel at exactly 1,728 in³ must return no DIM weight. A 48 × 40 × 50 in pallet at 600 lb must return 55.56 ft³, a density of 10.80 lb/ft³ and class 92.5. A 16 × 12 × 10 in case under a 60 in height limit must stack 9 per layer and 5 layers, 45 per pallet. If a case fails, the update does not ship.
Corrections
If you find a figure that disagrees with a current carrier publication, tell us through the contact page with the source. Confirmed errors are corrected in the dataset, which corrects every page that uses the figure, and the correction is noted here with its date.
What the figures are not
Results are estimates for planning and checking bills. Your carrier's measurement governs billing, and the NMFC item governs freight class. The site quotes weights, densities and counts, never prices, and it does not sell shipping. See the disclaimer.