Carriers charge for whichever is greater: a parcel's actual weight or its volumetric weight. This figure is the billable weight (also called chargeable weight).
Actual weight — the parcel's weight on a scale.
Volumetric weight — a weight calculated from the parcel's dimensions, reflecting how much space it takes up in transit.
A parcel that is large but light still occupies as much space on a vehicle or aircraft as a smaller, heavier one, so carriers bill on size as well as weight.
Billable weight = greater of (actual weight, volumetric weight)
This article covers international shipping services only.
How volumetric weight is calculated
Volumetric weight = (Length × Width × Height) ÷ Divisor
The divisor (also called the DIM factor) is set by the carrier. A lower divisor produces a higher volumetric weight, so it has a direct effect on shipping cost.
International divisors by carrier
Carrier | Services | Inches → lbs | cm → kg |
FedEx | International Priority, International Economy, International Connect Plus | 139 | 5,000 |
UPS | Worldwide Express, Worldwide Expedited, Worldwide Saver | 139 | 5,000 |
DHL Express | All international services | 139 | 5,000 |
⚠️ The 166 divisor sometimes quoted for UPS is a US-domestic retail counter rate and does not apply to international shipments.
Two things to watch for
1. 139 and 5,000 are not interchangeable
139 in³/lb and 5,000 cm³/kg are often quoted as if they were the same standard in different units, but they aren't:
139 in³/lb ≈ 5,721 cm³/kg
5,000 cm³/kg is therefore the stricter figure
Billing a shipment in kg at a 5,000 divisor produces roughly 14% higher volumetric weight than billing the same parcel in lbs at a 139 divisor. Where a carrier offers a choice of billing unit on an international lane, this is worth checking.
2. Rounding rules differ between carriers
Carrier | How rounding works |
FedEx | Each dimension is rounded up to the next whole inch/cm before dividing |
UPS | Each dimension is rounded up to the next whole inch/cm before dividing |
DHL Express | Divides on the measured dimensions, then rounds the final chargeable weight up to the nearest 0.5 kg |
⚠️ FedEx and UPS round every fractional dimension up before applying the formula. A box measuring 11.1 × 8.5 × 6.2 in is billed as 12 × 9 × 7 in. This is a common source of unexpected charges on carrier invoices.
Worked example
A carton measuring 40 × 30 × 25 cm with an actual weight of 4 kg:
Volume = 40 × 30 × 25 = 30,000 cm³
Volumetric weight = 30,000 ÷ 5,000 = 6 kg
Actual weight = 4 kg
Billable weight = 6 kg
The shipment is billed at 6 kg, despite weighing 4 kg, because the parcel is light relative to its size.
Why this matters
Shipping cost estimates based on actual weight alone understate cost for bulky or lightweight product categories, such as apparel, footwear, and homeware.
Reducing packaging size — right-sizing cartons and cutting void fill — is often the fastest way to lower billable weight and shipping cost.
Contracted divisors vary. High-volume shippers can negotiate more favourable divisors with their carrier (166, 194, 200+ on FedEx/UPS; DHL will move off 5,000 at volume). Check the divisor in your own carrier contract rather than assuming the standard rate applies.