Shipping costs aren’t just about weight anymore, but also size. As of August 18, 2025, UPS and FedEx now round up every fractional inch of a package before applying the dimensional weight (DIM) formula for small package services. This means that even a tenth of an inch can raise billable weight and trigger higher surcharges. USPS follows its own cubic pricing rules, but the message is the same: measurement precision has never mattered more. In turn, logistics professionals need platforms and processes that can keep up.
DIM Weight in 2025
The dimensional weight is: (L × W × H) ÷ DIM weight. Here’s a quick reference on how the major carriers now apply dimensional weight, and how the new rounding rules affect billing:
| Carrier | DIM Divisor | DIM Trigger | Updated 2025 Rounding Rule | Example of Impact |
| UPS & FedEx | 139 | All packages | Any fraction of an inch rounds up to the next whole inch. | If a box measures 8.2” high, it’s treated as 9”.
An 11 × 10 × 9 box = 990 in³ ÷ 139 = 7.12 lb, billed at 8 lb. |
| USPS | 166 | Only if package >1 ft³ (1,728 in³). Applies to Priority Mail and Ground Advantage. | Dimensions and weight round up to the next whole inch/pound. | A box 11.1 × 10 × 6 in = 666 in³ (<1 ft³), DIM does not apply.
USPS charges actual weight (3 lb). |
For example:
- A package’s actual measurements are 11.1" x 8.5" x 6.2
- DIM weight is 584.97 ÷ 139, which equals 4.20lbs
- The charge is only for 4.20lbs.
- The new rule measures them as 12” x 9” x 7”
- DIM weight is 756 ÷ 139, which equals 5.43lbs
- The new cost is now for 5.43lbs, an additional 1 lb increase
Until now, UPS often rounded dimensions down if the fraction was under half an inch, while FedEx used decimals; now both round up. Surcharges aren’t going away; they’re changing into an increase to billable weight.
Where Margins Get Squeezed
Some packages could face more changes than others from various factors, including:
● Light, bulky SKUs: Apparel basics such as bedding, pet supplies, and void‑filled picks get hit hardest for the amount of space they take, despite weighing very little.
● Threshold creep: Everyday items, such as curtain rods or rugs, can incur FedEx and UPS’s “additional handling” fees for boxes that cross the 48"/30" size thresholds. Packages that are over multiple dimensions could face significantly higher charging fees.
● Holiday premiumization: Holiday surcharges, combined with the rounding-up measurement, increase shipping prices during peak seasons.
● System mismeasurement: Outdated carton libraries, poorly calibrated scanners, or measuring boxes before sealing can all lead to dimensions that don’t match carrier billing. This could lead to systematic overcharges, which could quickly add up.
Margin Defense Playbook
With carriers changing the landscape for package pricing, shipments are at risk of higher costs. Here’s what businesses can do to protect their profit margins:
Packaging and Process
Use the smallest possible box or bag; shipping with a box that’s even 0.1 inches bigger can risk carriers rounding it up to increase the DIM weight. Businesses can switch to poly mailers instead of boxes, or consider investing in a box-on-demand machine, to custom-cut boxes to never overpay for empty space.
Another option is to update the carton library with smaller size increments so you always have the best fit.
Carrier and Service Choices
USPS offers cubic pricing on Priority Mail and Ground Advantage, letting businesses pay by cubic size instead of weight, an ideal solution for small, dense parcels. For other shipments, instead of opting for UPS or FedEx, regional carriers could be a more affordable alternative for short zones or ZIP codes with high surcharges. Zone-skipping can also cut costs by sending packages closer to their final destinations.
Tech Foundations
Update the order management system (OMS), warehouse management system (WMS), and checkout software to reflect the new rules. If your system incorrectly calculates 11.1" as 11", shipments can underquote and incur unexpected charges. Updating cartonization algorithms, which are the rules the system uses to determine which box to ship, can ensure that the best box is always selected.
Accounting for whole-inch rounding and USPS cubic breakpoints can reduce the chances of additional surcharges. Without the right tech, even the best packaging strategy can’t prevent extra charges.
Don’t Let The Platform Be The Bottleneck
The August 2025 rounding changes leave no room for error. A fraction of an inch can now tip shipments into higher billable weight, trigger additional handling fees, or push peak surcharges even higher. For e-commerce leaders, the lesson is clear: margin defense involves packaging, but also enhancing platforms and processes to work in sync. Re-measuring top SKUs, refreshing carton libraries, testing USPS cubic options, and calibrating dimensioners can help prevent systemic overbilling and help reclaim control of shipping costs.
Jerzy Zawadzki is the Chief Technology Officer at Polcode, where he’s been a key part of the team for over 16 years. With a deep focus on building the right environment for high-quality software projects, he ensures that teams have the structure, mindset, and support needed to deliver outstanding results. Jerzy is driven by the belief that technology should directly support the client’s business goals, turning ideas into scalable, effective solutions.
