Carriers charge for the space a parcel takes, not just its weight. A box of pillows weighs little but fills a van, so carriers bill a volumetric (dimensional) weight when it exceeds the real weight. The formula is one division, but the divisor depends on the carrier, and using the wrong one gives the wrong bill.
The formula
Volumetric weight = length x width x height / divisor. Measure the parcel’s outer dimensions at the widest points, including bulges. In centimetres and kilograms, common divisors are 5000 for international couriers, 6000 for standard air freight, and 4000 on some road and bulky-goods services. In inches and pounds, 139 is the standard US domestic divisor, with 166 surviving on some retail rates.
Billable (chargeable) weight = the greater of actual weight and volumetric weight, rounded up per the carrier’s rules. The carrier bills the larger number, never the smaller.
Worked examples
Parcel 50 x 40 x 30 cm, actual weight 4 kg. Volume = 60,000 cubic cm. At divisor 5000: 12 kg volumetric. At 6000: 10 kg. At 4000: 15 kg. In all three cases the volumetric weight beats the 4 kg actual weight, so the billable weight is 12, 10, or 15 kg depending on the service. The divisor alone swings the bill by 50% between the 4000 and 6000 cases.
Inches example: 20 x 16 x 12 inches = 3,840 cubic inches. At divisor 139: 27.6 pounds. If the parcel actually weighs 10 pounds, the billable weight is 27.6 pounds, rounded up per carrier rules. That is why a light, bulky parcel can cost triple what its scale weight suggests.
Per-piece versus per-shipment
Express couriers usually compare actual and volumetric weight per piece, then add the billable weights. Air freight forwarders often compare total actual weight with total volumetric weight for the whole shipment. The difference matters for mixed shipments: one heavy small box and one light big box can bill differently under the two methods. Check your carrier’s method before disputing a quote.
Also watch rounding: many carriers round each dimension up to the next whole inch or centimetre before calculating, and round the final weight up to the next half or whole kilo. A parcel measuring 11.9 inches is billed as 12 inches on such services.
Reducing the bill
Right-size the box: cutting height by a few centimetres can drop the volumetric weight a full kilo. Use mailers instead of boxes for soft goods, since mailers have no rigid volume. Cut void fill and let soft items compress. And negotiate: high-volume shippers can sometimes agree a higher divisor, which directly lowers every volumetric charge. Always confirm the divisor on your rate card; guides, including this one, summarise common values, but your contract rules.
Air, road, and sea use different rules
Air freight uses the 6000 divisor as its standard, while express couriers use 5000, which is why the same parcel bills heavier by courier than by air freight. Road services vary more, with some using 4000, especially for bulky goods where vehicle volume is the constraint.
Sea freight works differently again: less-than-container-load cargo is often charged by revenue ton, where 1 cubic metre equals 1,000 kg for charging purposes, and the carrier bills whichever is greater, weight or volume. The principle never changes, only the divisor: carriers always bill the scarcer resource, space or weight, whichever your parcel consumes more of.
Try it faster with the tool
You can follow every step above by hand, but the free Volumetric Weight Calculator — Dimensional Weight & Billable Weight (Divisors 5000 / 6000 / 4000) does the arithmetic for you. Enter your numbers and it gives the answer right away, so you can check your hand calculation or skip straight to the result.
Quick tips
- Volumetric weight = length x width x height / divisor.
- Billable weight = the greater of actual and volumetric.
- Confirm the divisor on your rate card; it swings the bill.