When the U.S. Postal Service (USPS) announced its rate hikes last year, there were some significant changes that went into effect in January. USPS has firmly established its dominant place in the eCommerce B2C delivery space so any rate change is likely to have an impact on shippers. But among the changes expected to have the most impact is how USPS will now calculate dimensional (DIM) weight.

Changes in USPS DIM weight calculations will especially impact those shippers who are still guessing about how to pack and ship parcels and may not have taken DIM rating into account when shipping through USPS. Previously, shippers could be a little less precise when it came to packing USPS shipments as DIM weighing only applied to Priority Mail shipped to Zones 5–9.

However, going forward, this won’t be the case.

USPS will no longer exempt shipments in Zones 1-4 from DIM rating. Parcels shipped Priority Mail, Parcel Select Ground, and Retail Ground over 1 cubic foot (1,728 cubic inches) to all zones will be subject to DIM pricing if the parcel exceeds 1 cubic foot. The removal of the Zone 1-4 exemption will have a particularly adverse effect on those retailers who are implementing omnichannel local delivery strategies.

To take it one step further, the calculation for DIM pricing will change from a divisor of 194 to 166, bringing it closer to those of other major parcel carriers. As a refresher, DIM weight is calculated by multiplying a package’s length, width, and height and applying the divisor. Beginning June 23, USPS will use the new formula for DIM weight which is (Length) X (Width) X (Height) /166.

The lower the divisor the more likely shipments will be rated according to DIM weight instead of actual weight. Bottom line: shippers that don’t take the air out of their cartons are going to see their shipping costs soar.

While these changes to dimensional pricing for USPS will have a real impact, other major carriers still apply dimensional pricing to more packages since they don’t limit it to packages of more than 1 cubic foot, and they use an even lower DIM divisor of 139.

As we mentioned in a previous blog, it’s difficult to know what to expect for DIM charges if you rely on guesstimates and rules of thumb for shopping cart rate calculations and order entry shipping quotes. With “free shipping,” the cost of guessing can result in reduced margins and disappointed customers.

Regardless of carrier, DIM weight rating can be less of a factor in your parcel shipping if you take the guesswork out of packing and harness the power of cartonization technology. Within seconds Transtream shipping software can determine the most transportation-cost effective packing process, saving you time and money while reducing waste.