How Dimensional Weight Affects Your International Shipping Cost

Every international shipment gets weighed twice. Once on a scale, for its actual weight, and once by a formula, for its dimensional weight. Dimensional weight (also called DIM weight or volumetric weight) estimates how much space a package takes up relative to how heavy it is. Carriers price by whichever number is greater, because a truck, ship, or plane has a limited amount of both weight capacity and physical space, and a large, light box uses up that space just as much as a small, heavy one.

If you’ve ever been surprised that a box full of pillows or packing peanuts cost more to ship than expected, dimensional weight is almost always the reason.

The formula is simple: multiply a package’s length by its width by its height, then divide by a carrier specific divisor.

• Inches and pounds: Length × Width × Height ÷ 139
• Centimeters and kilograms: Length × Width × Height ÷ 5000

The divisor represents an industry standard density assumption. Anything less dense than that assumption (in other words, anything bulkier for its weight) ends up with a dimensional weight that’s higher than its actual weight, and that’s the number you get billed for.

This is the part that trips people up. You don’t pay actual weight, and you don’t pay dimensional weight. You pay whichever one is greater, a figure called chargeable weight. A dense item, like books or tools, will usually be billed at its actual weight, since its dimensional weight comes out lower. A bulky, light item, like a lampshade or a stuffed animal collection, will usually be billed at its dimensional weight instead.

Say you’re shipping a box measuring 20 × 16 × 14 inches, and it weighs 18 pounds on the scale. Here’s the math:

• Actual weight: 18 lb
• Dimensional weight: (20 × 16 × 14) ÷ 139 = 4,480 ÷ 139 ≈ 32.23 lb

Since 32.23 is greater than 18, this shipment is billed at roughly 32.23 lb, not the 18 lb it actually weighs. Cutting the box down to something closer to the item inside it, say 16 × 12 × 12 inches, brings the dimensional weight down to about 16.55 lb, putting it back under actual weight and lowering the bill.

• Right size the box. Choose the smallest box your item and its padding can safely fit in, rather than reusing whatever box happens to be around.
• Use appropriate padding.Bubble wrap and packing paper protect an item without adding much volume. Loose fill peanuts, by contrast, often mean you’ve chosen a box that’s bigger than it needs to be.
• Consolidate multiple items. Combining several small items into one well fitted box usually beats shipping them separately in oversized ones.
• Flatten what you can. Furniture, luggage, and collapsible items should be broken down or folded before measuring, not measured in their bulkiest state.

You don’t need to run this math by hand. When you enter your package dimensions in our quote tool, chargeable weight is calculated automatically and instantly, using the same 139 (inches and pounds) and 5,000 (centimeters and kilograms) divisors described above, so the rate you see already reflects whichever weight applies. For a deeper breakdown, see our full guide to volumetric weight.

• Carriers bill by chargeable weight: the greater of actual or dimensional weight.
• Dimensional weight = Length × Width × Height ÷ 139 (in/lb) or ÷ 5,000 (cm/kg).
• Right sized boxes and minimal padding keep dimensional weight, and your cost, down.
• Our quote tool calculates chargeable weight for you automatically.