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Shipping weight, dimensional weight and how couriers charge

Send a box of pillows and you will be billed as though it weighed twenty kilograms. Couriers charge on whichever is greater — actual mass or dimensional weight — because van space runs out before payload does. Understanding the formula lets you predict the cost and, often, reduce it.

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How dimensional weight is calculated

Dimensional weight converts volume into a billable weight. Multiply length by width by height, then divide by a divisor set by the carrier. In metric the common divisor is 5,000 for centimetres, giving kilograms; in imperial it is 139 for inches, giving pounds.

A box measuring 40 × 30 × 30 cm has a volume of 36,000 cubic centimetres. Divided by 5,000 that is a dimensional weight of 7.2 kg. If the contents weigh three kilograms, you are charged for 7.2 — the higher figure always wins.

Divisors differ between carriers and between services, and that is where the money is. A divisor of 6,000 rather than 5,000 reduces the same box to 6 kg. Air freight typically uses 6,000, express parcels 5,000. When comparing quotes, check the divisor as carefully as the headline rate, and measure the box you will actually ship — including any padding — rather than the product inside it.

Key facts

Metric formula

Length × width × height in centimetres, divided by 5,000, gives kilograms.

Imperial formula

Length × width × height in inches, divided by 139, gives pounds.

Higher wins

You pay on actual or dimensional weight, whichever is greater.

Divisors vary

Air freight often uses 6,000, which lowers the billable figure for the same box.

Round up

Most carriers round dimensions to the next whole centimetre or inch before calculating.

Smaller boxes pay

Trimming five centimetres from each side of a 40 cm cube cuts volume by roughly a third.

How to get it right

1

Measure the packed box

Take the outside dimensions with the parcel sealed and padded.

2

Calculate the volume

Multiply the three dimensions together.

3

Divide by the divisor

Use 5,000 for centimetres to kilograms, or 139 for inches to pounds.

4

Compare and convert

Take the greater of actual and dimensional weight, then convert units if your carrier bills in the other system.

Questions people ask

A billable weight derived from the parcel's volume. Carriers use it so that light but bulky shipments pay for the space they occupy.

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