I quote and book air and ocean freight most working days, and the one line on a rate sheet that ambushes shippers more than any other is chargeable weight. A pallet of throw cushions can read 40 kg on the warehouse scale and still get billed as if it weighed close to 90. The scale is not lying and neither is the carrier. Air and sea carriers bill on whichever is greater, your actual gross weight or the volumetric weight of the space your cargo occupies, because a light bulky consignment wastes the capacity someone else could have paid for. Once you understand how that second number is built, freight invoices stop being a mystery and start being something you can plan around.
This guide walks through the exact formulas for air freight and less-than-container-load (LCL) ocean freight, with worked examples you can copy for your own boxes. Every divisor here is checked against the published rules, so you can take the arithmetic to a carrier and it will hold up.
Why carriers bill the greater of two weights
An aircraft hold and an ocean consolidation box both run out of room long before they run out of lifting capacity. Feathers, foam mattresses, empty plastic housings and light apparel fill a container while barely moving the scale. If carriers charged those loads by gross weight alone, a shipper could book an entire pallet position for the price of a few kilograms. To keep pricing tied to the resource that actually gets consumed, which is cubic space, the industry converts volume into a notional weight and then compares it against what you really put on the scale.
The higher of the two figures becomes your chargeable weight. In our experience quoting air freight, roughly seven out of ten commercial shipments end up billed on volume rather than gross weight, and the ratio climbs for e-commerce parcels. That is not the carrier padding the bill. It reflects how much emptier a hold gets when the cargo is bulky.
Air freight: the IATA 6000 divisor
For general air cargo, the volumetric standard comes from the International Air Transport Association (IATA), codified in its TACT (The Air Cargo Tariff) rules. You take the box dimensions in centimetres, multiply length by width by height to get cubic centimetres, then divide by 6000:
- Volumetric weight (kg) = (L cm x W cm x H cm) / 6000
- The 6000 divisor is equivalent to a density of 167 kg per cubic metre, because one cubic metre holds 1,000,000 cm3 and 1,000,000 / 6000 rounds to 166.67.
- Working in inches and pounds instead, the equivalent divisor is 366.
Maersk's air cargo guidance and virtually every forwarder tariff cite the same 6000 figure, so it is safe to treat 6000 cm3/kg as the baseline for scheduled air freight unless a specific carrier tells you otherwise. One more habit matters, and it varies by carrier. Under standard IATA practice airlines round the final chargeable figure up to the next half kilogram, so a shipment that calculates to 43.31 kg is billed at 43.5 kg, and 43.6 kg would round to 44.0 kg. Some carriers and most express services round up to the next whole kilogram instead, which would push that same 43.31 kg to 44 kg. Confirm the rounding rule with your carrier before you model the cost.
Worked example: a three-carton air shipment
Say you are flying three identical cartons of lightweight electronics enclosures. Each carton measures 55 cm by 35 cm by 45 cm and weighs 10 kg on the scale. Here is the full calculation.
| Metric | Value |
| Cartons | 3 |
| Dimensions (each) | 55 x 35 x 45 cm |
| Volume (each) | 86,625 cm3 |
| Total volume | 259,875 cm3 (0.26 CBM) |
| Gross weight | 30 kg |
| Volumetric at 6000 (IATA air) | 43.31 kg, rounded to 43.5 kg |
| Volumetric at 5000 (express) | 51.98 kg, rounded to 52.0 kg |
| Chargeable weight (IATA air) | 43.5 kg |
Step by step: 55 x 35 x 45 gives 86,625 cm3 per carton, and three of them come to 259,875 cm3. Divide by 6000 and you get 43.31 kg, which rounds up to 43.5 kg. The gross weight is only 30 kg. Because volumetric beats gross, the airline bills 43.5 kg. Your 30 kg of product travels on a 43.5 kg ticket, and that gap is entirely about the air inside the boxes.
Ocean freight: FCL versus LCL, and the revenue ton
Sea freight splits into two worlds. Full-container-load (FCL) means you rent a whole box, most often a 20-foot or 40-foot unit, at a flat rate. Once you have paid for the container, chargeable weight barely matters until you approach a payload or road-legal axle limit, so FCL pricing is about how well you fill the box you already bought. That is why heavy, dense cargo usually wants FCL, and why so much of the volume moving through the world's busiest container ports travels in sealed full boxes rather than shared ones.
LCL is where a volumetric rule reappears, because you are sharing a consolidation container with other shippers and paying only for the slice you use. Ocean consolidators price LCL on the revenue ton, also written R/T or W/M for weight or measure. The rule, as iContainers and other consolidators publish it, compares one cubic metre against one metric ton:
- Chargeable revenue tons = the greater of total CBM or total gross weight in metric tons
- One CBM is set equal to 1000 kg, so the break-even density is 1000 kg per cubic metre
- Most consolidators apply a one revenue-ton minimum and bill in 0.1 increments above that
Because typical mixed cargo runs somewhere between 200 and 500 kg per cubic metre, volume wins the comparison for the overwhelming majority of LCL bookings. Only genuinely dense freight, think ceramic tiles or bottled liquids, tips the balance so that weight governs.
Worked example: a six-pallet LCL shipment
Picture six standard pallets of packaged apparel. Each pallet footprint is 1.2 m by 1.0 m, built up to 1.1 m tall, and the whole consignment weighs 1,650 kg gross. Run the W/M comparison.
- Volume per pallet: 1.2 x 1.0 x 1.1 = 1.32 CBM
- Total volume: 1.32 x 6 = 7.92 CBM
- Gross weight: 1,650 kg, which is 1.65 metric tons
- Revenue tons: the greater of 7.92 and 1.65, so 7.92 R/T
The measurement figure wins comfortably, and you are billed on 7.92 revenue tons. If the port-to-port LCL rate were, say, 85 US dollars per revenue ton, the ocean-freight line alone would come to 673.20 dollars before the origin and destination fees that consolidators add on top. The density here works out to 208 kg per cubic metre (1,650 divided by 7.92), which sits right in the range where volume dominates.
Now flip it. Suppose instead you ship 2.5 CBM of machine castings weighing 3,200 kg. Gross weight is 3.2 metric tons against 2.5 CBM, so the greater figure is 3.2, and you pay for 3.2 revenue tons. The cargo is dense enough (1,280 kg per cubic metre) that weight finally governs. Working out both scenarios before you book is the single fastest way to sanity-check an LCL quote, and it is also where you decide whether the load has grown big enough to justify a full container instead.
Parcel and courier: why the divisor is different
If you also ship by express courier, brace for a harsher number. Integrators publish their own dimensional divisors, and they are tighter than the IATA air standard. DHL's published tariff, along with UPS and FedEx international express, uses 5000 cm3/kg in metric, which corresponds to a density of 200 kg per cubic metre. In inches and pounds the same carriers apply a divisor of 139, and USPS uses 166. The tighter the divisor, the more a bulky parcel is penalised.
Look back at the three-carton example. Under the express divisor of 5000, the same 259,875 cm3 calculates to 51.98 kg, which rounds up to 52.0 kg, versus 43.5 kg under the IATA air rule. Identical boxes, different books, an 8.5 kg swing. That is why I always ask which divisor a rate is built on before comparing an express quote against a consolidated air-freight quote. Comparing the prices without checking the divisors is how shippers talk themselves into the wrong lane.
| Service type | Metric divisor | Density equivalent | Rounding |
| IATA air freight (general cargo) | 6000 cm3/kg | 167 kg/m3 | up to next 0.5 kg |
| Express / courier (DHL, UPS, FedEx intl) | 5000 cm3/kg (139 for in/lb) | 200 kg/m3 | up to next 0.5 kg |
| USPS domestic | 166 (in/lb) | roughly 200 kg/m3 | up to next lb |
| Ocean LCL (W/M) | 1 CBM vs 1000 kg | 1000 kg/m3 break-even | 0.1 R/T, 1 R/T minimum |
How to cut your chargeable weight
Once you can see where the volumetric penalty comes from, most of the fixes are about squeezing air out of the shipment. A few that consistently move the invoice:
- Right-size the carton. A box with 8 cm of empty headspace is 8 cm of billed volume. Cutting a 45 cm carton down to 37 cm on our earlier air example would drop volumetric weight by roughly 18 percent.
- Increase density. Nesting and flat-packing raise kilograms per cubic metre and push the comparison back toward gross weight, where you are usually charged less.
- Weigh the palletisation trade-off. Palletising protects cargo and speeds handling, but the pallet itself adds height and deck weight. On light freight that extra volume can raise the chargeable figure, so run the numbers both ways.
- Consolidate timing. Combining several small LCL bookings into one can clear the one revenue-ton minimum more efficiently and sometimes crosses the threshold where FCL becomes cheaper per unit.
- Mind the last mile. Denser, fewer pallets also cut handling at the port, which feeds into drayage and yard costs downstream.
When you request a quote on GetTransport.com, the chargeable weight is computed for you from the dimensions and weight you enter, using the divisor that matches the mode. Seeing that figure before you commit means you can test a different carton size or a different service without waiting for a carrier to come back with a surprise.
Where the money actually leaks
The biggest overspend I see is not a miscalculated divisor. It is shippers optimising the freight rate while ignoring the volumetric multiplier and the accessorials attached to it. A slightly cheaper per-kilo air rate on a bulky load loses to a higher rate on a denser one every time, because the chargeable weight, not the headline rate, decides the total. On the ocean side, the same discipline applies to the ground moves around the terminal, where chassis shortages and port dwell can add more than the freight itself. And for air specifically, routing through one of the busiest cargo airports often buys you frequency and competition on price that a thin secondary lane cannot match. Do the volumetric math first, then negotiate. That order matters more than any single rate.
Frequently asked questions
What is chargeable weight in simple terms?
It is the weight a carrier actually bills you on, defined as the greater of your gross (scale) weight and your volumetric weight. Volumetric weight converts the cubic space your cargo occupies into a notional weight, so light bulky shipments pay for the room they take up rather than for what they weigh.
Why is the air freight divisor 6000 but couriers use 5000?
The 6000 cm3/kg figure is the IATA standard for general air cargo, equal to 167 kg per cubic metre. Express integrators such as DHL, UPS and FedEx set a tighter 5000 cm3/kg (200 kg per cubic metre, or 139 in inches and pounds) because parcel networks are even more space-constrained, so the same box is billed as heavier in the express channel.
Does chargeable weight apply to full-container (FCL) sea freight?
Not in the same way. FCL is priced per container at a flat rate, so volumetric weight is largely irrelevant until you hit a payload or axle limit. The revenue-ton (W/M) rule, comparing one CBM against 1000 kg, applies to LCL, where you share a container and pay only for your share.
How do I calculate volumetric weight for air freight?
Multiply length by width by height in centimetres, then divide by 6000 for standard air freight. Compare the result with your gross weight and take the higher one. Then round up to the next half kilogram. For example, 259,875 cm3 divided by 6000 is 43.31 kg, billed as 43.5 kg.
What is a revenue ton in LCL shipping?
A revenue ton (R/T), also called W/M, is the billing unit for LCL ocean freight. You take the greater of your total cubic metres or your total metric tonnes. Six pallets at 7.92 CBM weighing 1.65 tonnes are billed on 7.92 revenue tons, because the volume figure is larger than the weight figure.
Can I be charged on actual weight instead of volume?
Yes, whenever your cargo is dense enough. If gross weight exceeds the volumetric or revenue-ton figure, the scale weight governs. That happens with heavy freight like metal castings or bottled liquids, roughly above 167 kg per cubic metre for air and 1000 kg per cubic metre for LCL.