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Dimensional weight is the carrier's way of charging for space, not just weight. A large light box takes up the same room in a truck or plane as a small heavy one, so carriers compute a volume-based weight and charge whichever is higher: the actual scale weight or the dimensional weight. Shrinking the box is the cheapest way to cut the bill.
They measure the box (length times width times height), take the volume, and divide by a carrier-specific divisor to get a weight equivalent. Then they compare that number to the actual scale weight and charge the higher of the two. The divisor differs by carrier and by service: express services typically use a smaller divisor, which punishes bulky boxes more.
You can't look up one universal divisor. Each carrier sets its own, and domestic and international divisors differ, so the same box can have a different dimensional weight at Canada Post than at a courier. That's why identical parcels get different quotes from different carriers.
Trucks and planes run out of space before they run out of weight capacity: they "cube out" before they "weigh out." A truck full of pillows weighs almost nothing but earns the carrier almost nothing if priced by weight alone. Dimensional pricing charges for the scarce resource, which is space. That's why a box of pillows can cost as much to ship as a box of books.
| Shipment | Actual weight | Dimensional weight | You pay for |
|---|---|---|---|
| Pillows in a big box | Light | High | The dimensional weight |
| Books in a small box | Heavy | Low | The actual weight |
| Shoes in the retail box | Medium | Medium | Whichever edges higher |
| Anything in an oversized box | Whatever it is | Inflated | The inflated dimensional weight |
The classic trap is void fill. Packing peanuts, air pillows, and crumpled paper add almost no weight but lots of volume, so over-boxing a small item in a big box with lots of filler is the most expensive way to ship it.
LetterAgent shipping labels are flat-rate Canada Post Xpresspost, so there's no dimensional-weight math on your end: the quote is the quote. Canada-only, 5 kg max.
Ready to ship it? Get a shipping label with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and get your label.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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