Offix Edge sells shipping on five different companies. They are:

FedEx (both Express and Ground)
DHL (International shipping only, no shipping within the USA.)
U.S. Post Office
SF Express (a very reputable Chinese shipping company.)

The U. S. Post Office prices packages by weight only, regardless of the size of the package.

The other four companies price shipping by comparing “actual weight” to “dimensional weight.” Then they charge you for whichever one is higher. This is how it works:

First they weigh your package to get the “actual weight.” Let’s say that your box weighs 7 pounds.

Now they calculate the “dimensional weight.” First, they measure the length, width, and the height of the box. These measurements are rounded up to the next whole inch. For example, if your box is 14 & 1/2 inches by 12 & 3/4 inches by 7 & 1/8 inches, the measurements are rounded up to 15 inches by 13 inches by 8 inches. Those measurements are used in a “dimensional weight” calculation as follows:

15 inches times 13 inches times 8 inches equals 1,560 cubic inches.

FedEx and SF Express divide 1,560 inches by 166 cubic inches per pound to arrive at a “dimensional weight” of 9.39 pounds. This is then rounded up to 10 pounds.

UPS and DHL divide 1,560 inches by 139 cubic inches per pound to arrive at a dimensional weight of 11.22 pounds, which is rounded up to 12 pounds.

So even though your box actually weighs 7 pounds, you will be charged for a heavier shipment due to the size of the box. The package companies justify this by saying that you are taking up more space in their trucks and airplanes by using too large a box, so they are charging you for the extra space.

IF that same box had an actual weight of 20 pounds, in other words it weighs more than the calculated dimensional weight, then you would be charged for the actual weight: 20 pounds.

Whichever method gets them more money is how you are going to be charged.

The “Dimensional Weight” formula:

(L x W x H)
—————————— = Dimensional Weight (lbs)
(cubic inches per pound)

The moral of the story: IT COSTS MONEY TO SHIP EMPTY SPACE FILLED WITH AIR (or packing paper, or peanuts, or bubble wrap, etc.)

Yes, Amazon and other retailers send tiny things in big boxes. They do so much shipping that they can tell the package companies that they will not pay for dimensional weight, they will just change to another shipper. The package companies do not want to lose their business so they do not apply the dimensional weight to retailers. We private parties get to subsidize the whole mess.

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