Dimensional Weight: Why Big, Light Boxes Cost More

Couriers charge for the space a parcel takes up, not just its weight. A large box of pillows can cost more to ship than a small box of books. The calculation behind this is dimensional weight, also called volumetric weight.

The formula

The divisor is set by each carrier and service. Common examples:

• Inches and pounds: 139 or 166
• Centimeters and kilograms: 5,000 or 6,000

Always check your carrier's current divisor, because it differs between services and changes over time.

Billable weight

The carrier compares the actual weight with the dimensional weight and charges for whichever is higher.

Example (centimeters and kilograms, divisor 5,000): a 50 × 40 × 30 cm box weighing 4 kg has a dimensional weight of 60,000 ÷ 5,000 = 12 kg. You'll be billed for 12 kg, three times the actual weight. Carriers usually round measurements and weights up, too.

Cutting the cost

• Use the smallest box that protects the item; every centimeter counts on all three sides.
• Stock boxes sized for your best sellers instead of a few generic sizes.
• Consider padded mailers or poly bags for soft, unbreakable goods.
• Measure accurately before booking to avoid adjustment charges later.

Freight and pallets

Larger shipments use similar ideas. Freight may be priced by volume, by weight or by density, depending on the mode and region. For pallets, measure the full loaded height, including the pallet itself.

Converting units

If your carrier works in kilograms but you measure in inches, convert first: 1 inch = 2.54 cm and 1 kg ≈ 2.205 lb. Using a divisor with the wrong units is a common and expensive mistake.