The Complete Guide to Dimensional (Volumetric) Weight
By Arshi Khan, Founder of Just4Marketing · Last reviewed October 2026
Carriers charge by space as well as weight. A large, light parcel takes up room in a truck or plane that could carry something heavier, so carriers calculate a 'dimensional weight' from its size and bill whichever is higher. This guide shows how dimensional weight is calculated, how billable weight is rounded, and how to keep shipping costs down with the right box.
How box size changes the bill (divisor 139, 4 lb item)
| Box (inches) | Dimensional weight | Billable weight |
|---|---|---|
| 10 × 8 × 6 | 3.45 lb | 4 lb (actual) |
| 12 × 10 × 8 | 6.91 lb | 7 lb (size) |
| 16 × 12 × 10 | 13.81 lb | 14 lb (size) |
Cutting dimensional weight charges
Use the smallest box that protects the item
Shaving an inch off each side can save more than lighter packaging ever will.
Consider poly mailers
Soft goods like clothing ship well in mailers that add almost no volume.
Check every new product
Run new SKUs through the calculator before setting shipping prices, especially bulky but light items.
Frequently asked questions
How is dimensional weight calculated?
Multiply the package's length × width × height and divide by the carrier's DIM divisor. In inches and pounds, a common divisor is 139; in centimetres and kilograms, 5000 is common. A 12 × 10 × 8 inch box is 960 ÷ 139 = 6.91 lb.
What is billable weight?
It's the weight you're charged for: the higher of the actual weight and the dimensional weight, rounded up. In the example, a 4 lb item in that box is billed as 7 lb.
Why do I enter the divisor myself?
Divisors vary by carrier, service, and account. Some services use 166 instead of 139, some international services use 6000, and negotiated contracts can differ. Use the figure on your own rate card.
Should I measure to the nearest inch?
Measure the longest point of each side, including any bulges. Many carriers round each dimension to the nearest whole inch or centimetre before calculating, so a few millimetres can change the billable weight.