How to use the dimensional weight calculator
- 1Choose whether you measure the box in inches or centimetres, then enter its length, width and height at the widest points.
- 2Leave side rounding on if your carrier rounds each measurement up to a whole inch or centimetre.
- 3Choose pounds or kilograms and enter the weight of the packed box.
- 4Pick an example DIM divisor or type the one from your carrier’s current rate guide or contract.
- 5Read the billable weight, which one applies, and how much extra weight the box size adds.
What dimensional weight is
Dimensional weight, also called DIM or volumetric weight, is a weight a carrier works out from the size of a parcel. A truck or plane fills up by space as well as by weight, so a large, light box takes room that could have carried heavier, better-paying parcels. DIM pricing makes sure the carrier is paid for that space.
You find it by multiplying length, width and height and dividing by a number called the DIM divisor. With inches the result is in pounds; with centimetres it is in kilograms. A smaller divisor gives a higher DIM weight, so a carrier that lowers its divisor is effectively raising prices on bulky parcels.
DIM weight (lb) = Length × Width × Height (in) ÷ Divisor (in³/lb) DIM weight (kg) = Length × Width × Height (cm) ÷ Divisor (cm³/kg)
Billable weight: the greater of the two, rounded up
Carriers compare the actual weight with the DIM weight and charge for whichever is greater. That figure is the billable weight. Most US carriers round each weight up to the next whole pound, so 18.13 lb is billed as 19 lb. This calculator rounds up to the next whole pound or kilogram. Some international carriers round to the next 0.5 kg instead, so check your carrier’s rules for light parcels.
Many carriers also round each side up to the next whole inch before multiplying. USPS, for example, started rounding fractional inches up in July 2026. Leave side rounding on unless your carrier measures to the fraction.
When you enter dimensions in inches and weight in kilograms (or the reverse), the calculator converts the actual weight to match the divisor, since a divisor in in³/lb gives pounds and one in cm³/kg gives kilograms.
Billable weight = Round up (greater of Actual weight and DIM weight)
Common DIM divisors (examples to verify)
These figures were checked in November 2026 from carrier announcements and shipping industry reports, not from every carrier’s current tariff. Divisors differ by carrier, service, country and account, and negotiated contracts often use a different number. Treat them as examples and confirm yours in your carrier’s service guide or your shipping software.
139 (in³/lb): used by UPS and FedEx for most US domestic and international daily rates, and by USPS from July 12, 2026 for Priority Mail, Priority Mail Express, Ground Advantage and Parcel Select. USPS applies DIM pricing only to parcels larger than 1 cubic foot (1,728 cubic inches).
166 (in³/lb): the older USPS divisor, now replaced by 139 for both retail and commercial USPS prices, though some contract and older rate cards still use it. 5000 (cm³/kg): widely used for international express parcels, including by DHL Express. 6000 (cm³/kg): an example of a divisor some carriers and freight forwarders use; check your own carrier’s rate guide.
Why an oversized light box costs more
Take a 6 lb product in an 18 × 14 × 10 inch box. With a 139 divisor its DIM weight is 18.13 lb, so you pay for 19 lb even though the box weighs 6. Thirteen pounds of the charge are for air.
The fix is usually the box, not the product. Trimming an inch or two from each side, using poly mailers for soft goods, and keeping a few box sizes rather than one big one can drop many parcels back to their actual weight. The "largest volume billed at actual weight" figure shows the biggest box you can use before size starts to cost you.
Largest volume at actual weight = Billable actual weight × Divisor
Worked example
An online store ships a 6 lb pillow in an 18 × 14 × 10 inch box with a carrier that uses a 139 divisor.
| Box volume | 2,520 in³ |
| DIM weight (2,520 ÷ 139) | 18.13 lb |
| Actual weight | 6 lb |
| Which applies | Dimensional weight |
| Billable weight (rounded up) | 19 lb |
| Same box with a 166 divisor | 15.18 lb, billed as 16 lb |
The parcel is charged as 19 lb, 13 lb more than it weighs. At actual weight, the largest box billed as 6 lb would be 834 in³ (6 × 139), about a 12 × 10 × 7 inch box. In metric, a 40 × 30 × 20 cm box at a 5000 divisor is 4.8 kg, billed as 5 kg.