UPS bills whichever number is larger: the reading on the scale, or a size-based weight worked out from the outside of the carton. The arithmetic is public, and so is the divisor, which UPS states as 139 for Daily Rates and 166 for Retail Rates (per ups.com, checked 2026-07-28).
A carton that grows without gaining weight still climbs the rate card, and the scale never tells you.
Everything below is lifted from the UPS shipping dimensions and weight page, read on 2026-07-28. Nothing here is our interpretation.
We put the identical 5 lb of household goods into three cartons and quoted each one from Newark, NJ 07102 to Atlanta, GA 30303 on 2026-07-28. Only the box changed. The prices below are the whole amount a customer pays at checkout, with our charge already inside.
| Carton | Cubic inches | Scale weight | Size weight at 139 | UPS Ground | Window returned |
|---|---|---|---|---|---|
| 12 x 10 x 6 in | 720 | 5 lb | 6 lb | $14.05 | 2-3 business days |
| 18 x 14 x 10 in | 2,520 | 5 lb | 19 lb | $23.70 | 2-3 business days |
| 24 x 18 x 14 in | 6,048 | 5 lb | 44 lb | $36.75 | 2-3 business days |
One service, one route, one weight, and a spread of $22.70 between the small carton and the large one. The scale never moved. What moved was 5,328 cubic inches of extra air, which the divisor turns into 38 phantom pounds. Run the same cartons through 166 instead and the size weights land at 5 lb, 16 lb and 37 lb, which is why knowing which rate type you are on changes the answer.
We also quoted that largest carton loaded properly. A 24 x 18 x 14 in box holding 50 lb came back at $45.01 on UPS Ground with the same 2-3 business day window, on the same route, on the same day. Adding 45 real pounds to the box cost $8.26. Growing the box while holding the weight at 5 lb cost $22.70. Air is the more expensive input.
UPS names Daily Rates and Retail Rates as separate rate types with separate divisors, and the page we read does not define which shipper falls into which. That ambiguity is the practical reason to price a specific box on a specific day rather than reason your way to a number.
UPS Ground Saver quoted $13.52 for the small carton and $20.50 for the middle one, both cheaper than Ground. Neither row carried a transit window on this capture, so we print the price and leave the timing column empty rather than invent one.
The published ceiling is 150 lb and 165 inches of length and girth combined, with a single side capped at 108 inches. Past that the shipment is not a dimensional weight problem any more, it is a freight problem.
UPS states two: 139 for Daily Rates and 166 for Retail Rates, per its shipping dimensions and weight page read on 2026-07-28. Length times width times height goes over whichever divisor applies, and any fraction in the answer rounds up to the next whole pound.
Yes. UPS applies it across all of its domestic and international package services with no size exemption, which is the main way it differs from USPS. A 12 x 10 x 6 in carton is 720 cubic inches, so it rates as 6 lb at the 139 divisor even when the scale reads 5.
On our 2026-07-28 capture, a fixed 5 lb went from $14.05 to $36.75 on UPS Ground, Newark to Atlanta, purely by moving from a 12 x 10 x 6 in carton to a 24 x 18 x 14 in one. Same weight, same service, same day, $22.70 apart.
Heavy and small, usually. The 24 x 18 x 14 in carton holding 50 lb quoted $45.01 on UPS Ground, while the same carton holding 5 lb quoted $36.75. Forty-five extra pounds added $8.26, because the size-based weight was already doing the pricing.