USPS dimensional weight: when the box size sets the price

Enter the length, width and height of the box and its real weight: the calculator applies the USPS dimensional weight rule and prices the box in your zone.

Independent site, not the Postal Service: prices read in its own price files.

Packed, box included. Up to 70 lb

Example: an 18 x 14 x 12 inch box weighing 5 lb· change a figure to see yours

Weight the Postal Service charges

22 lb

Size weight 22 lb (3,024 cubic inches ÷ 139) against 5 lb on the scale

Priority Mail, zone 8, Post Office$122.15
Same box if size did not count$39.00
Ground Advantage, same box$87.30
Length plus girth70.0 in
How this is computed

Compiled by Radif Partners · How the prices are built

USPS dimensional weight applies to Priority Mail, Priority Mail Express and Ground Advantage parcels larger than one cubic foot, 1,728 cubic inches, in every zone. The Domestic Mail Manual rounds each side up to a whole inch, multiplies length by width by height, divides the result by 139 and rounds up to the next pound; the Postal Service then charges the higher of that size weight and the real weight, never more than the 70-pound price. A box of 18 by 14 by 12 inches holds 3,024 cubic inches: its dimensional weight is 22 pounds. Filled with 5 pounds of pillows and sent by Priority Mail to zone 8, it costs $122.15 at a counter, against $39.00 if only the scale counted. Ground Advantage charges $87.30 for the same box. A box of exactly 12 by 12 by 12 inches stays under the rule. Light, bulky items are where the rule bites: the smaller the box, the lower the price.

USPS dimensional weight for common box sizes

The table prices a few boxes by Priority Mail in zone 8 at a counter. The billed weight is the higher of the size weight and the real weight. Note the jump between the 12-inch cube and the same cube one inch taller.

Rule of the Domestic Mail Manual (sections 113, 123, 133); Notice 123 prices in force today.
Box and real weightCubic inchesSize weightBilled weightPriority Mail, zone 8
12 x 12 x 12 in, 3 lb1,728none3 lb$28.10
12 x 12 x 13 in, 3 lb1,87214 lb14 lb$86.10
16 x 12 x 10 in, 4 lb1,92014 lb14 lb$86.10
18 x 14 x 12 in, 5 lb3,02422 lb22 lb$122.15
20 x 16 x 14 in, 8 lb4,48033 lb33 lb$198.15
24 x 18 x 18 in, 10 lb7,77656 lb56 lb$259.30

Fees on top of the size weight

Two more charges can apply to a large box. A parcel longer than 22 inches pays a length fee, larger above 30 inches; a parcel over two cubic feet pays a volume fee. The calculator adds them when you enter the size. Above 108 inches of length plus girth, the size limits page explains what is still accepted.

Dimensional weight of another box

Example: an 16 x 12 x 10 inch box weighing 4 lb· change a figure to see yours

Weight the Postal Service charges

14 lb

Size weight 14 lb (1,920 cubic inches ÷ 139) against 4 lb on the scale

Priority Mail, zone 8, Post Office$86.10
Same box if size did not count$33.95
Ground Advantage, same box$57.65
Length plus girth60.0 in
Back to the full calculator at the top →

To bring the price down, pick a box that just fits the item and measure it after closing, since a bulging side counts. Round each side up to the next whole inch, as the manual asks, or check a flat rate box if the item is dense. The shipping cost calculator also takes the size under More details.

Questions people ask before they mail

Tap a question to see the answer.

How do I calculate USPS dimensional weight?

Measure the box in inches, rounding each side up to the next whole inch. Multiply length, width and height. If the result is over 1,728 cubic inches, divide it by 139 and round up to a whole pound: that is the dimensional weight. The price is the higher of the dimensional weight and the real weight, up to the 70-pound price.

Do flat rate boxes have dimensional weight?

No. A Priority Mail flat rate box or envelope costs its flat price whatever it weighs up to 70 pounds and whatever its zone, so neither the real weight nor the size weight changes it. That is one reason a dense, heavy item travelling far can be cheaper in a flat rate box.

Does dimensional weight apply to small boxes?

No. Up to one cubic foot, 1,728 cubic inches, the Postal Service charges the real weight only. A 12 by 12 by 12 inch box is exactly one cubic foot and stays under the rule; adding one inch to any side puts it over. Long thin boxes can also pay length fees above 22 inches.

Next steps

Package size limits

70 pounds, 108 and 130 inches, and the fees for long or bulky boxes.

Flat rate box prices

Envelope, small, medium and large box: today, online and in 2027, and when each one wins.

Cost to ship a package

Every USPS service for your weight and ZIP Codes, at the counter and online, today and in 2027.

Heavy packages (20 to 70 lb)

Twenty to seventy pounds: Ground Advantage, Priority Mail, flat rate and Media Mail compared.

Postal Service price files, manual chapters and filings behind this page (4)

Each price, rule and zone was read in these documents on November 13, 2026.

Compiled by

Independent publisher of US parcel price tables built from the Postal Service's Notice 123 price files and its domestic zone chart. Paid by no carrier: no commission, no affiliate link, no paid placement.

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Prices are read from the Postal Service price files, never estimated. They leave out pickup, special handling, hazardous material and any extra service you add at the counter. The January 17, 2027 prices are proposed and await review by the Postal Regulatory Commission.