What is dimensional weight?

A pricing weight carriers compute from a package's volume: length × width × height in inches divided by a divisor. If it is higher than the actual weight, you pay for the dimensional weight. It exists because a big light box takes truck space that a dense box of the same weight does not.

Which divisor do USPS, UPS and FedEx use in 2026?

USPS moved to 139 on 12 July 2026. UPS uses 139 on Daily Rates (account shippers) and 166 on Retail Rates for domestic shipments. FedEx uses 139 for US, Puerto Rico and international shipments. The table names the rate type each row assumes and links the carrier's own rule page.

Does USPS always apply dimensional weight?

No. USPS only applies it to packages larger than one cubic foot (1,728 cubic inches). A 12 × 12 × 12 box is exactly one cubic foot and is still billed at actual weight; a 13 × 12 × 12 box is not.

How is the result rounded?

USPS rounds each side up to the next whole inch; UPS and FedEx round each side to the nearest whole inch (UPS with a one-inch minimum). All three divide and round up to the next whole pound, and USPS caps dimensional weight at 70 lb. Actual weight is also rounded up to the next pound, and you are billed on the larger of the two.

How do I lower dimensional weight?

Use the smallest box that protects the item, cut down oversize boxes, switch to a padded mailer or soft pack where the item allows it, and for USPS keep the package at or under one cubic foot. The box size calculator shows the dimensional consequence of each stock box.

Dimensional Weight Calculator

One set of dimensions, three carriers. See the billable weight USPS, UPS and FedEx will each charge for the same box, with the 2026 divisor, the USPS one-cubic-foot threshold and the rounding rules applied the way the carriers apply them.

Rates verified Nov 6, 2026Source: USPS DMM 283.1.4 and 223.1.4 — Dimensional weight

Package

Length

Width

Height

Actual weight

Billable weight by carrier

USPS (Ground Advantage, Priority Mail)6 lb
14 × 12 × 10 = 1680 in³, not over 1,728 in³ (1 cubic foot), so USPS bills the actual weight of 6 lb.
UPS (Daily Rates)13 lb
14 × 12 × 10 = 1680 in³ ÷ 139 = 12.09 → 13 lb dimensional; actual 6 lb; billable 13 lb.
UPS (Retail Rates, domestic)11 lb
14 × 12 × 10 = 1680 in³ ÷ 166 = 10.12 → 11 lb dimensional; actual 6 lb; billable 11 lb.
FedEx (Express and Ground)13 lb
14 × 12 × 10 = 1680 in³ ÷ 139 = 12.09 → 13 lb dimensional; actual 6 lb; billable 13 lb.

How billable weight is worked out

Carriers charge on whichever is greater: the package’s actual weight or its dimensional weight. Dimensional weight is the box volume in cubic inches divided by the carrier’s divisor. With a 139 divisor, every 139 cubic inches of box counts as one pound, so a 20 × 16 × 12 inch box (3,840 cubic inches) is treated as 28 pounds even if it holds a pillow.

Carrier rules this calculator applies

Carrier	Divisor	Applies when	Rounding	Status
USPS (Ground Advantage, Priority Mail)	139	volume over 1,728 in³ (1 cubic foot)	each side up to the next inch; weight up to the next pound; capped at 70 lb	verified from the carrier's rules
UPS (Daily Rates)	139	every package	each side to the nearest inch; weight up to the next pound	verified from the carrier's rules
UPS (Retail Rates, domestic)	166	every package	each side to the nearest inch; weight up to the next pound	verified from the carrier's rules
FedEx (Express and Ground)	139	every package	each side to the nearest inch; weight up to the next pound	verified from the carrier's rules

Worked example

A 14 × 12 × 10 inch box weighing 6 lb has a volume of 1,680 cubic inches. On UPS Daily Rates: 1,680 ÷ 139 = 12.09, rounded up to 13 lb, which beats the 6 lb actual weight, so the label is priced at 13 lb; on UPS Retail Rates it is 1,680 ÷ 166 = 10.12 → 11 lb. For USPS the box is not over one cubic foot, so no dimensional weight applies and the label is priced at 6 lb. Change the box to 14.2 × 12.2 × 10.2 and USPS rounds each side up to 15 × 13 × 11 = 2,145 cubic inches, which is over the threshold: 2,145 ÷ 139 = 15.4 → 16 lb. That is a difference most sellers never see until the carrier adjustment lands on the invoice.

Why the July 2026 USPS change matters

USPS raised its dimensional divisor from 166 to 139 effective 12 July 2026, which increases dimensional weight by about 19% for every oversize package. Many calculators still divide by 166 and under-quote the postage. This page uses 139 and records the date the rule was checked.

Questions sellers ask

What is dimensional weight?: A pricing weight carriers compute from a package's volume: length × width × height in inches divided by a divisor. If it is higher than the actual weight, you pay for the dimensional weight. It exists because a big light box takes truck space that a dense box of the same weight does not.
Which divisor do USPS, UPS and FedEx use in 2026?: USPS moved to 139 on 12 July 2026. UPS uses 139 on Daily Rates (account shippers) and 166 on Retail Rates for domestic shipments. FedEx uses 139 for US, Puerto Rico and international shipments. The table names the rate type each row assumes and links the carrier's own rule page.
Does USPS always apply dimensional weight?: No. USPS only applies it to packages larger than one cubic foot (1,728 cubic inches). A 12 × 12 × 12 box is exactly one cubic foot and is still billed at actual weight; a 13 × 12 × 12 box is not.
How is the result rounded?: USPS rounds each side up to the next whole inch; UPS and FedEx round each side to the nearest whole inch (UPS with a one-inch minimum). All three divide and round up to the next whole pound, and USPS caps dimensional weight at 70 lb. Actual weight is also rounded up to the next pound, and you are billed on the larger of the two.
How do I lower dimensional weight?: Use the smallest box that protects the item, cut down oversize boxes, switch to a padded mailer or soft pack where the item allows it, and for USPS keep the package at or under one cubic foot. The box size calculator shows the dimensional consequence of each stock box.

Related calculators

Sources and verification dates

USPS DMM 283.1.4 and 223.1.4 — Dimensional weight — checked Nov 6, 2026, in effect since Jul 12, 2026Applies to parcels over 1 cubic foot addressed to zones 1–9. Each side is rounded up to the next whole inch, the product divided by 139 and rounded up to the next pound; if the result exceeds 70 lb the 70-lb price applies. Nonrectangular parcels multiply the volume by 0.785 first.
UPS — Determine dimensional weight (Rate and Service Guide) — checked Nov 6, 2026Each side rounded to the nearest whole inch (minimum 1 in); divide by 139; any fraction of a pound rounds up. Applies to every package; billable weight is the greater of actual and dimensional.
FedEx — What is dimensional weight? — checked Nov 6, 2026FedEx: multiply length by width by height in inches, rounding each measurement to the nearest whole inch, and divide by 139 for US, Puerto Rico and international shipments. Billed on the greater of dimensional and actual weight; fractions of a pound round up.

Every value on this page is read from the linked official pages on the date shown. If a platform changes a fee, the change log records the old and new values and the effective date.