Carriers do not bill on what your package weighs. They bill on whichever is bigger, the actual weight or the volume of the box converted to weight. Build the box you ship today on the left. Build a smaller version on the right. See what shrinking the box would save you in a year.
The box you actually ship in.
The smallest version you could ship in.
Your dim divisor is fixed by your carrier. Your overall shipping cost is not. Part n Parcel works with Canadian merchants to bring down the full bill, dim weight included, by routing volume through pooled carrier agreements and managing the parts of the invoice merchants do not have time to read line by line.
Take the length, width, and height of your box in inches. Multiply them together to get the volume in cubic inches. Purolator Ground uses a published cube factor of 12.4 pounds per cubic foot, which is the same as dividing your volume by 139 cubic inches per pound. The result is your dim weight in pounds.
Whichever is bigger, your actual weight or your dim weight, is what the carrier bills you on.
Carriers round every dimension up to the next whole inch (or whole centimetre) before doing the dim weight math. A box that measures 14.2 inches gets billed as if it were 15. Every fraction of an inch on every side adds to your bill. That is why the rounded numbers in this calculator turn orange when they jump.
Prices use the Purolator Rate Guide, September 2025, Ground service, same-province delivery. We picked one carrier and one lane to keep the math honest. Other carriers price differently, but the gap between your actual weight and your dim weight will look roughly the same across all of them.
Same-province delivery is the example lane shown for the math. We picked one lane so the numbers are reproducible against the published rate guide. If you ship heavily across provinces or to remote regions, your real dim weight cost is larger than what you see here.
Not on a single parcel. The cube factor is set by the carrier and the service you ship on. What you can change is which carrier and service handle your volume, and how that volume gets priced. That is the part of the bill Part n Parcel manages on behalf of Canadian merchants.
No. The calculator uses Purolator's published list rates as a reference point. Your real cost reflects your account discount, fuel surcharge, taxes, home address fees, and any other charges on your invoice. The dollar amounts here size the dim weight impact of your box, not your total bill. Use this to understand how your box changes your bill, not to predict the bill itself.
