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Dimensional weight calculator for U.S. & Canada carriers
The ÷ number is the carrier's DIM divisor — your package volume is divided by it to get dimensional weight.
Enter a length, width and height greater than zero.
Dimensional divisors by carrier
Each carrier divides your package volume by a set number to get dimensional weight. A bigger divisor means a lower dimensional weight — and USPS only applies its divisor above one cubic foot.
Updated for the USPS July 12, 2026 divisor change.
United States (in³ per lb)
Metric (cm³ per kg)
Divisors, size thresholds and dimensional-weight rules are set by each carrier and are subject to change at any time without notice. Figures are estimates for guidance only — Rollo Ship applies each carrier's live rules and confirms billable weight before you print a label.
Dimensional weight (DIM weight), also called dimensional shipping weight, reflects how much space a package takes up rather than how heavy it is. Carriers bill on the greater of DIM weight and actual weight. This free calculator returns the DIM weight for USPS, UPS, FedEx, Canada Post and Purolator across the U.S. and Canada, rounding your dimensions the way carriers measure them.
How dimensional weight works
Dimensional weight turns a package's size into a billable weight. Here's the math, and the DIM weight for common box sizes.
Carriers price by volume because a truck or plane runs out of room before it runs out of weight capacity, so a big, light box still takes up paid space. That is why dimensional shipping weight exists, and why a smaller box almost always lowers the price.
Measure and round
Measure length, width and height. USPS and UPS round each fraction up to the next whole inch. FedEx is rounded to the nearest whole inch, and metric dimensions to the nearest whole centimetre. Rounding first is what makes your figure match the invoice.
Multiply for volume
Multiply the rounded length, width and height together. A 12 × 12 × 12 in box is 1,728 cubic inches.
Divide by the carrier divisor
Divide volume by the carrier's DIM divisor and round the result up. USPS uses 139 but only above one cubic foot; UPS and FedEx use 139 at every size.
DIM weight = (Length × Width × Height) ÷ carrier divisor
| Box size | Volume | ÷139 |
|---|---|---|
| 10 × 10 × 10 in | 1,000 in³ | 8 lb USPS n/a, under 1 ft³ |
| 12 × 12 × 12 in | 1,728 in³ | 13 lb USPS n/a, exactly 1 ft³ |
| 14 × 14 × 14 in | 2,744 in³ | 20 lb |
| 16 × 12 × 12 in | 2,304 in³ | 17 lb |
| 18 × 14 × 12 in | 3,024 in³ | 22 lb |
| 20 × 16 × 12 in | 3,840 in³ | 28 lb |
Dimensional weight rounded up to the next whole pound, the way carriers bill. USPS, UPS daily rates and FedEx all divide by 139. USPS applies that figure only above one cubic foot, so the two smallest boxes are n/a for USPS and are billed on actual weight. UPS domestic retail, including The UPS Store, divides by 166 instead. UPS daily rates and FedEx apply it at every size. Divisors and thresholds vary by service and date; figures are estimates for guidance only. Rollo Ship applies each carrier's live rule and confirms billable weight before you print.
Dimensional vs billable weight
Dimensional weight is what your box's size weighs. Billable weight is what you actually pay: the greater of dimensional weight and your real scale weight. Big, light packages get billed on size, not weight.
This is the dimensional half. Add your scale weight in the billable weight calculator for the final number.
DIM weight is a number. You want a price.
Dimensional weight is one input. What you pay also depends on carrier, service and zone. Rollo Ship prices the same package on USPS, UPS, FedEx, Canada Post and Purolator, at discounted rates, before you print.
No credit card. No monthly subscription.
Rollo Ship is a shipping system that combines rate comparison, label generation and order management in one place, applying each carrier's dimensional-weight rules — for USPS, UPS, FedEx, Canada Post and Purolator — before you print. It is not a carrier; it gives shippers carrier choice without lock-in, on web, iOS and Android. Rollo Ship is rated 4.8 on Capterra (23 reviews). More than 500,000 shippers across the U.S. and Canada use Rollo.
More shipping tools
Free calculators from Rollo Ship.
Big box, light contents? DIM weight sets the price.
Rollo Ship is the free multi-carrier shipping platform for shippers across the U.S. and Canada. It applies dimensional-weight rules for USPS, UPS, FedEx, Canada Post and Purolator, then shows the discounted rate on each before you print.
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Dimensional weight FAQ
What shippers ask about DIM weight.
What is dimensional weight?
Dimensional (DIM) weight reflects how much space a package takes up rather than how heavy it is. It's length x width x height divided by a carrier divisor. Carriers bill on whichever is greater, the dimensional weight or the actual weight.
How do I calculate dimensional weight?
Round each dimension the way the carrier measures, then multiply for volume and divide by the carrier's divisor. A 12 x 12 x 12 in box is 1,728 cubic inches; divided by 139 that is about 12.4 lb, which rounds up to 13 lb. USPS does not apply dimensional weight at exactly 1,728 cubic inches. This calculator does the math for USPS, UPS, FedEx, Canada Post and Purolator.
What divisor does each carrier use?
In the U.S., USPS uses 139 above one cubic foot. UPS daily rates use 139 at every package size; UPS domestic retail, including The UPS Store, uses 166, and UPS export retail uses 139. FedEx uses 139. In Canada, Canada Post and Purolator use roughly 6000 cubic centimetres per kilogram, and metric international air uses 5000. Divisors vary by service and date.
Does USPS charge dimensional weight on small boxes?
No. USPS applies dimensional weight only to packages over one cubic foot, which is 1,728 cubic inches, on applicable services. A 10 x 10 x 10 in box is 1,000 cubic inches, so it is billed on actual weight. UPS and FedEx apply dimensional weight at every size.
Do carriers round my package dimensions?
Yes, and it depends on the carrier. USPS rounds each dimension up to the next whole inch, so a fraction such as 12.1 in is measured as 13. UPS rounds each fraction up the same way: 1.1 in is measured as 2. FedEx is rounded to the nearest whole inch here, so 12.4 in is measured as 12 and 12.6 in as 13. Metric dimensions are rounded to the nearest whole centimetre. This calculator rounds the same way for the carrier you pick, which is why its figure lines up with the invoice.
When does dimensional weight apply?
When it's larger than the actual weight, and when the package clears the carrier's size threshold. Large but light packages are usually billed on dimensional weight, while small dense ones are billed on actual weight. The billable weight calculator compares both.
How do I reduce dimensional weight?
Use the smallest box that safely fits the item, cut excess void fill, and avoid oversized packaging. A smaller box lowers volume, which lowers dimensional weight and the price you're billed. Dropping one inch off each side of a 14 in cube removes about 15 percent of the volume.
How do you measure the girth of a box?
Girth is the distance around the thickest part of a parcel: girth = 2 x (width + height), using the two shorter sides. Carriers add length plus girth to flag oversize packages and surcharges, separately from dimensional weight. This calculator shows the figure alongside your DIM weight.
Do UPS and FedEx use the same dimensional weight?
Yes on whole-inch boxes at U.S. daily rates. Both use a 139 cubic inch per pound divisor and apply dimensional weight at every package size, so the DIM weight matches. UPS rounds each fraction of an inch up, and FedEx is rounded to the nearest inch here, so a fractional side can differ. USPS also uses 139, but only above one cubic foot, and it rounds each dimension up.
Can I use an online tool to determine my parcel's dimensional weight?
Yes. This free DIM weight calculator returns your parcel's dimensional weight instantly: enter length, width and height and pick the carrier, no account needed. For the billable figure and a live discounted rate, Rollo Ship compares USPS, UPS, FedEx, Canada Post and Purolator before you print.
Is the calculator free?
Yes, with no account needed. Rollo Ship has no monthly subscription. Your first 200 labels have no service fee (carrier postage still applies), then it's 5 cents per label, down to 1 cent at the VIP tier of Rollo Rewards.