Dimensional weight: how carriers bill light, bulky boxes

What is dimensional weight?

Dimensional weight, often shortened to dim weight or DIM weight, is the weight a carrier assigns to a package based on how much space it takes up. A box of pillows weighs little but fills a truck the same way a box of books does, so carriers charge for the space.

Every major US carrier compares two numbers: the actual weight on the scale and the dimensional weight from the box size. FedEx states that you are charged on the dimensional weight or actual weight, whichever is greater. USPS and UPS work the same way. The higher number is called the billable weight, and it is what the price table is read against.

USPS applies dimensional weight only to parcels larger than 1 cubic foot (1,728 cubic inches). Below that size, USPS charges the actual weight. FedEx applies the comparison to every shipment, and UPS says dimensional weight may apply to all UPS domestic and international package services, so a small, light box can still be billed above its scale weight with them.

How to calculate dimensional weight: the formula

The dimensional weight formula is the same for every carrier. Only the divisor and the rounding rules change.

1. Measure the box in inches

   Measure the outside of the box: length (the longest side), width and height. USPS says any fraction of an inch must be rounded up to the next whole inch. FedEx rounds each measurement to the nearest whole inch.

2. Multiply length by width by height

   The result is the cubic size of the box in cubic inches. For USPS, check it against the threshold: dimensional weight applies only to parcels larger than 1 cubic foot (1,728 cubic inches). For a nonrectangular Ground Advantage Commercial parcel, the Domestic Mail Manual multiplies this result by 0.785 first.

3. Divide by the carrier's divisor

   Divide the cubic inches by the divisor: 139 for USPS, 139 for FedEx, and for UPS 139 for Daily Rates or 166 for Retail Rates. The result is the dimensional weight in pounds.

4. Round up and compare

   UPS says: Increase any fraction to the next whole pound. USPS rounds the dimensional weight up to the next whole number, and for Ground Advantage Commercial, if the dimensional weight is over the weight limit, the customer pays the 70-pound price. Compare the result with the actual weight. The higher of the two is the billable weight. USPS Ground Advantage is charged by the pound up to 70 lbs (rounded up).

Dimensional weight divisors: USPS, UPS and FedEx

A larger divisor gives a lower dimensional weight, so the divisor decides how much a carrier charges for space. USPS and FedEx publish one divisor. UPS uses a different divisor for retail rates and for daily rates, so check which rate type your label is bought at.

USPS dimensional weight for commercial labels follows the same rule. The Domestic Mail Manual says Ground Advantage Commercial parcels over the threshold are priced on the actual weight or the dimensional weight, whichever is greater. If you leave out the dimensions when you buy the label, or enter wrong ones, USPS charges a dimension-noncompliance fee. USPS cubic pricing is a different way of pricing small parcels and is covered in the USPS cubic pricing guide.

Worked examples: pillows, plush, lampshades, wreaths and framed art

These examples use USPS Ground Advantage Retail rules: divisor 139, dimensions rounded up to the whole inch and weight rounded up to the pound. The box sizes and actual weights are example inputs, not measurements of real products.

1. Example: a throw pillow

   Example: an 18 x 18 x 8 inch box weighing 2 lb on the scale. 18 x 18 x 8 = 2,592 cubic inches, which is over one cubic foot. 2,592 divided by 139 is 18.6, rounded up to 19 lb. USPS bills 19 lb, not 2 lb. At the Ground Advantage Retail prices dated July 12, 2026, zone 5 is $14.10 for 2 lb and $33.80 for 19 lb.

2. Example: a plush toy in a small box

   Example: a 12 x 10 x 8 inch box weighing 1 lb. 12 x 10 x 8 = 960 cubic inches, under one cubic foot, so USPS bills the actual 1 lb. At UPS retail rates, 960 divided by 166 for Retail Rates is 5.8, rounded up to 6 lb. At FedEx, 960 divided by 139 is 6.9 lb, well above the 1 lb on the scale.

3. Example: a lampshade

   Example: a 16 x 16 x 14 inch box weighing 3 lb. 16 x 16 x 14 = 3,584 cubic inches, so USPS bills 26 lb (3,584 divided by 139 is 25.8). The box is also more than 2 cubic feet (3,456 cubic inches), which adds a nonstandard fee of $21.00.

4. Example: a dried-flower wreath

   Example: a 24 x 24 x 8 inch box weighing 2 lb. 24 x 24 x 8 = 4,608 cubic inches, so USPS bills 34 lb. The 24 inch side adds the length fee of $4.50, and the volume adds $21.00, because the fee for volume exceeding 2 cubic feet applies in all cases. A 20 x 20 x 6 inch box would be 2,400 cubic inches, 18 lb billable, with no length fee and no volume fee.

5. Example: a framed print

   Example: a 28 x 22 x 4 inch box weighing 6 lb. 28 x 22 x 4 = 2,464 cubic inches, so USPS bills 18 lb. The 28 inch length adds $4.50. Length plus girth is 28 + 2 x (22 + 4) = 80 inches, well inside the USPS limit.

USPS package size limits and weight limit

The USPS weight limit is 70 pounds for a single package. Priority Mail lists a maximum of 70 lbs. The USPS Ground Advantage weight limit is the same: packages are charged by the pound up to 70 lbs (rounded up).

The USPS max package size is measured as length plus girth. Length is the longest side, and girth is the distance around the thickest part, so for a box it is twice the width plus twice the height. The general limit is 108 inches in length and girth combined. Priority Mail allows 108 inches. USPS Ground Advantage Retail allows 130 inches in length and girth combined.

A Ground Advantage Retail parcel that measures more than 108 inches but not more than 130 inches in length and girth pays the oversized price, regardless of weight. In the price list dated July 12, 2026, that runs from $112.10 in zone 1 to $294.25 in zones 8 and 9. Compare UPS and FedEx prices for the same box before you buy.

There is also a minimum. USPS letters and pieces up to a quarter inch thick must be at least 5 inches long, 3-1/2 inches high, and 0.007-inch thick. Parcels must be large enough to hold the following required items on a single optical plane, meaning the address, return address, label, postage and barcode fit on one side.

USPS nonstandard fees for long, large and odd packages

USPS adds nonstandard fees on top of the postage for packages that are hard to sort by machine. They are separate from dimensional weight, so a light, bulky box can pay both. Ground Advantage and Priority Mail charge different amounts. The large volume fee applies to parcels more than 2 cubic feet (3,456 cubic inches).

If a package has both a nonstandard shape and a length fee, you only pay the higher nonstandard fee, not both. The volume fee is the exception: the fee for volume exceeding 2 cubic feet applies in all cases. Nonstandard shapes include tubes, rolls and other mailable items (including polybags) with contents that may shift.

How to ship oversized items

Start with the box. Most dimensional weight is empty space, so the cheapest fix is a box that fits the product. Compress pillows and plush in a vacuum bag before boxing them, ship wreaths in the shallowest box that protects them, and nest lampshades of different sizes in one carton.

If the package is too big or too heavy for USPS, UPS and FedEx take larger parcels. UPS accepts 150 lbs, 108 inches in length and 165 inches in length and girth combined. FedEx Ground accepts packages up to 150 lbs., 108" in length, and 165" in length plus girth. For heavier loads, UPS points to its freight service for a shipment weighing over 150 lbs.

Price the same box with each carrier before you buy a label. USPS ignores dimensional weight under one cubic foot and UPS and FedEx may not, so the cheapest carrier changes with the size of the box.

Reused boxes and poly mailers

You can ship in a reused box. The USPS rule is: Any obsolete marking on a container to be reused for mailing must be obliterated. Cover or black out old labels and barcodes so the box is not misrouted.

Poly mailers are measured like boxes: measure the filled mailer at its longest, widest and thickest points. A soft mailer packed with a pillow or plush toy can stay under the USPS one cubic foot threshold, which means USPS bills the actual weight. Ground Advantage can charge the $4.00 nonstandard fee on other mailable items (including polybags) with contents that may shift, so pack them firm and flat.

Where Nation fits

Questions about dimensional weight