Dimensional weight (also called volumetric weight) is the weight a carrier assigns to your parcel based on the space it takes up. You calculate it by multiplying length × width × height, then dividing by the service’s divisor. The carrier bills whichever is higher: the actual weight or the dimensional weight. So a light but bulky box can cost as much as a heavy one.
What is dimensional weight?
A truck fills up by volume as much as by weight. To make a large, light parcel pay for its space, carriers convert the box’s volume into a theoretical weight: the dimensional weight. They then compare it with the actual weight on the scale, and the higher of the two becomes the billable weight.
It is the most common reason a shipment costs more than expected: the parcel was weighed, but nobody measured the box.
The formula
Metric: (length × width × height in cm) ÷ divisor = dimensional weight in kg. Imperial: (length × width × height in inches) ÷ divisor = dimensional weight in lb. Measure the closed, packed box at its widest point, bulges included.
The divisor depends on the carrier and the service. For example, Canada Post uses 5,000 for Xpresspost and 6,000 for Regular Parcel (in cm and kg). The smaller the divisor, the higher the dimensional weight. A contract account can also have its own divisor.
| Element | What it is | What to check |
|---|---|---|
| Dimensions | Length, width and height of the packed box | Measure at the widest point |
| Divisor | Number set by the carrier for each service | Read the divisor for the chosen service |
| Actual weight | Weight of the parcel on the scale | Weigh the whole parcel, packaging included |
| Billable weight | The higher of actual or dimensional | Compare both before you pay |
A worked example
Take a 40 × 30 × 30 cm box that weighs 4 kg. Its volume is 36,000 cm³.
- With a divisor of 5,000: 36,000 ÷ 5,000 = 7.2 kg. The billable weight is 7.2 kg, not 4 kg.
- With a divisor of 6,000: 36,000 ÷ 6,000 = 6 kg. The billable weight is 6 kg.
- In a 40 × 30 × 20 cm box, the same contents come to 24,000 cm³, or 4.8 kg with a divisor of 5,000: about a third less billable weight.
Want to run the numbers on your own boxes? Our free dimensional weight calculator (/tools/dimensional-weight) takes centimetres or inches and a custom divisor.
How to reduce dimensional weight
- Pick the smallest box that still protects the product: every centimetre counts, because it is multiplied by the other two dimensions.
- Cut the empty space: less bubble wrap and loose fill, more snug-fitting protection.
- For soft goods (clothing, textiles), a padded mailer or poly bag can replace a box.
- Keep a small set of standard box sizes and save them: you enter the right dimensions on every shipment without measuring again.
- Compare services: the divisor changes from one to another, so the same parcel can have a different billable weight.
Divisors, rounding rules and oversize fees vary by carrier, service and account. Nothing in this guide is a rate or a carrier commitment: confirm the billable weight and the price at the quote step, for your parcel.
See the real price before you buy the label
MesColis is not a carrier. When you create a shipment, you enter the weight and packed dimensions, and we show the carriers and services that serve your lane side by side, each with its total price for that parcel. Dimensional weight is therefore already built into the comparison, and your saved boxes are one click away on the package step.
With a free MesColis account, no contract and no minimum volume, you compare the carriers that serve your lane before you buy the label.