How shipping costs are calculated
International carriers charge by more than just the weight of your package — the size of the box matters just as much. A small, dense box might be cheap to ship; the same weight in a large, light box might cost three times more.
This page explains how dimensional weight works, how to calculate it, and how to keep your shipping costs as low as possible. If you have a specific question, email us at [email protected].
What is dimensional weight?
When you ship internationally, the carrier needs to decide what to charge you. The obvious answer is scale weight — put the package on a scale, read the pounds, multiply by the rate. But that misses something important.
An aircraft has a fixed amount of cargo space. A small, heavy box and a large, light box can both weigh five pounds on the scale, but the large box takes up far more room in the hold. If carriers only charged by weight, they would lose money every time someone shipped a big box full of pillows or polystyrene.
To solve this, carriers use dimensional weight (also called “volumetric weight”). It converts the size of your package into an equivalent weight, so a bulky-but-light box is priced fairly for the space it occupies.
How dimensional weight is calculated
The formula is straightforward. Measure the longest side (length), the next side (width), and the height of the box in inches. Multiply them together, then divide by a fixed number called the dimensional factor.
The dimensional factor used by Hadship and our partner air carriers is 139 when measurements are in inches.
So a box that measures 20 × 16 × 12 inches works out to: 20 × 16 × 12 ÷ 139 = 27.6 lb dimensional weight. If that same box only weighs 7 lb on the scale, the carrier will still charge you for 27.6 lb because the size is what determines how much space it takes on the plane.
Which weight does the carrier charge?
The rule is simple: the carrier charges whichever is greater — the actual scale weight, or the dimensional weight. Whichever number is higher wins.
For small, heavy items (a hard drive, a watch, a stack of books), scale weight is usually higher and that is what you will pay. For light, bulky items (a winter jacket, a pair of trainers in their box, a small appliance with foam padding), dimensional weight is usually higher and that is what you will pay.
A few services do not apply dimensional weight at all and charge purely by scale weight. We will always show every available rate at checkout so you can pick the cheapest carrier for your specific package.
How to reduce dimensional weight
You can lower your shipping cost by reducing the size of the box your items travel in. The quickest wins:
- Request re-packing at our warehouse. Many retailers ship items in oversized boxes filled with air pillows or crumpled paper. Our team can transfer the contents to a smaller, snugger box that ships at a much lower dimensional weight.
- Consolidate packages. If you have several packages from different retailers, combining them into one box almost always reduces the total volume — and you only pay for one international shipment instead of several.
- Remove unnecessary packaging. Retailer marketing inserts, hang tags, oversized hangers, and decorative outer boxes add space without adding value. We can strip these before sending.
- Pick the right carrier at checkout. For light but bulky items, a carrier that charges by scale weight only may be cheaper. We show every available rate so you can pick the best one for each shipment.
If you have a specific shipment in mind and want help estimating the dimensional weight before you buy from a retailer, email us at [email protected] and our team will be happy to advise.
