The weight on your freight invoice often doesn’t match the weight on your packing list. That’s not an error. Air, express and ocean carriers bill on chargeable weight, and for light, bulky cargo that figure is set by how much space the shipment takes up rather than by what it weighs.
Chargeable weight isn’t what the scale says
An airline has two limits on every flight: how much weight the aircraft can lift and how much room there is in the hold. IATA puts it simply: a ton of feathers takes up far more space than a ton of steel, and carriers price that space.
So the carrier works out two numbers and bills on the higher one:
- Actual weight is the measured weight of the shipment, which is its gross weight: the goods plus all packaging, and the pallet if you ship on one.
- Volumetric weight is a weight calculated from the dimensions, reflecting the space the shipment occupies.
Chargeable weight = the actual weight or the volumetric weight, whichever is higher.
If the actual weight is equal to or greater than the volumetric weight, chargeable weight and gross weight are the same (before rounding). If not, you pay for more kilograms than the shipment weighs. On the air waybill, the weight in the rate calculation box is either the gross weight or the volume weight.
The names get mixed up, so it helps to sort them into two groups. Dimensional weight, dim weight and volume weight all mean volumetric weight, the size-based figure. Billed weight means chargeable weight, the figure the charge is based on. They aren’t interchangeable: one is an input to the comparison, the other is its result.
The divisor: how volume becomes kilograms
To turn a shipment’s size into a weight, carriers divide its volume by a fixed number. For air freight, the formula is:
Volumetric weight (kg) = length × width × height (cm) ÷ 6,000
IATA describes 6,000 cm³ per kg as the general rule for air cargo. TACT (The Air Cargo Tariff and Rules) is the industry’s reference work for airline rates and rules, but each airline publishes its own tariff, and that’s where to check the exact terms for your shipment.
Express services use a smaller number. Major express carriers (UPS, for example) divide cm³ by 5,000.
Ocean LCL works on a different basis but comes to the same kind of comparison. Each cubic meter counts as 1,000 kg, and the freight is charged per cubic meter or per 1,000 kg (one metric ton), whichever is greater. In divisor terms, that’s 1,000 cm³ per kg. A “measurement ton” is 40 ft³ in US usage and 42 ft³ in UK usage; this guide and our calculators use 1 m³.
The smaller the divisor, the more kilograms the same volume turns into, and the harder it hits light cargo. Ranked by the weight one cubic meter converts to, ocean (1,000) comes first, express (5,000) second and air (6,000) last:
| Mode | Divisor (cm³/kg) | 1 m³ counts as | 9.6 m³ / 800 kg shipment billed at |
|---|---|---|---|
| Air freight (IATA general rule) | 6,000 | about 167 kg (166.67) | 1,600 kg |
| Express (e.g., UPS) | 5,000 | 200 kg | 1,920 kg |
| Ocean LCL (per m³ or per 1,000 kg, whichever is greater) | 1,000 equivalent | 1,000 kg | 9.6 m³, equivalent to 9,600 kg |
This is why a per-kg rate on its own tells you little. Two quotes can show the same rate per kg and still produce different bills, because the rate is multiplied by a different number of kilograms. Before comparing, ask which weight the rate applies to and which divisor produced it. If you’re still deciding between modes, see sea vs. air freight.
One box, then a hundred
Take one box measuring 60 × 40 × 40 cm and weighing 8 kg, the same example used in our guide to CBM. Its volume is 96,000 cm³, or 0.096 m³.
- Air: 96,000 ÷ 6,000 = 16 kg, twice the actual weight. The calculator shows a chargeable weight of 16.0 kg.
- Express: 96,000 ÷ 5,000 = 19.2 kg, exactly 2.4 times the actual weight. Rounded up to the next 0.5 kg, the calculator shows a chargeable weight of 19.5 kg.
- Ocean LCL: 0.096 m³, equivalent to 96 kg. At this size a minimum charge may apply, so check the quote for one.
Now ship 100 of the same box. The CBM calculator gives 9,600,000 cm³, or 9.6 m³, with an actual weight of 800 kg. By air that’s billed as 1,600 kg, by express as 1,920 kg, and by ocean LCL as 9.6 m³, equivalent to 9,600 kg.
Worked example: 42 boxes of flat-pack shelving
Here’s a common type of air booking. An importer is bringing in 42 boxes of flat-pack shelving, each 55 × 45 × 35 cm and 11 kg. The packing list says 462 kg.
Each box is 86,625 cm³, so the shipment is 3,638,250 cm³, about 3.64 m³. Divided by 6,000, that’s a volumetric weight of 606.375 kg, roughly 606 kg. Before anything else happens, the chargeable weight is already about 31% above the packing list weight, some 144 kg more. The calculator shows a chargeable weight of 606.5 kg.
Then the boxes go through a dimensioner (an automated measuring device) and come out at 56 × 46 × 36 cm: bulging has added 1 cm to each dimension. That’s 92,736 cm³ per box and 3,894,912 cm³ in total, for a volumetric weight of 649.152 kg, about 649 kg. The calculator figure becomes 649.5 kg, which is about 40% above the 462 kg on the packing list and another 43 kg on top of the booked figure.
Two measuring rules explain how this happens:
- Dimensions are taken at the extreme points. Carriers measure the longest, widest and highest point of each package, bulges and overhang included. For an irregular shape, that means the length, width and height of the smallest box that would fit around it.
- Fractions are handled differently by each carrier. Korean Air’s tariff rounds each dimension to the nearest centimeter, up or down. UPS’s own guidance mentions both rounding up to the next whole number and rounding to the nearest whole number. Don’t assume every measurement gets rounded up. In this example the extra centimeter comes from the boxes bulging, not from rounding.
The fine print: weight breaks, divisors and rounding
Weight breaks and rate classes
The air freight charge is the chargeable weight multiplied by the applicable rate. If that comes to less than the minimum charge, you pay the minimum.
Airline general cargo rates are split into rate classes:
- M: the minimum charge (the lowest amount billed regardless of weight).
- N: the normal rate, for shipments under 45 kg (or under 100 kg where the airline has no 45 kg rate).
- Q: quantity rates, from 45 kg upward.
Within Q, rates are set in weight breaks (weight brackets with lower per-kg rates). Typical breaks in airline rate tables are under 45 kg, 45 kg, 100 kg, 300 kg and 500 kg. The per-kg rate drops as you move into a higher break.
That creates an edge case. Say the chargeable weight is 480 kg. By weight it falls in the band below 500 kg, which carries the higher per-kg rate. Airlines apply the lower charge from a higher weight category: if 500 kg at the 500 kg rate costs less than 480 kg at the higher rate, you’re charged for 500 kg at the lower rate, and the air waybill can show the 500 kg break weight. That’s how the total charge can fall even though chargeable weight never drops below actual weight.
Cargo shipped in a full unit load device (ULD) can be priced per unit instead. Under a bulk unitization program (BUP), called BUC (bulk unitization charge) in some airline tariffs, there’s a minimum charge per sector and ULD type, plus an excess weight charge for anything over the pivot weight, which is the most weight the minimum charge covers. For ULD types and sizes, see our guide to air freight ULDs.
Divisors differ by carrier and service
The 6,000 and 5,000 figures are common, not universal. Divisors vary by carrier, service and country, and some airlines apply 5,000 to air freight too.
In the US, carriers work in inches and pounds. UPS divides cubic inches by 139 for Daily Rates and by 166 for Retail Rates to get the dimensional weight in pounds. A factor of 139 in³/lb is about 5,022 cm³/kg, close to the 5,000 used elsewhere.
Carriers can change their factors, so check the current service guide, the carrier’s published terms and rates, before relying on a figure. If you ship on contract terms, check whether they set a different divisor; you can enter a custom divisor in the chargeable weight calculator.
Rounding and minimum charges
Airlines set a minimum charge for each sector, so a small shipment may pay the minimum whatever it weighs.
The chargeable weight itself is also rounded up. Airline tariffs such as Korean Air’s round it up to the next 0.5 kg. For express, UPS in the UK rounds up to the next 0.5 kg and UPS in the US to the next whole pound. Our calculator rounds air and express results up to the next 0.5 kg. LCL shipments may also carry a minimum charge, so check the quote.
On a small shipment, the minimum charge and the rounding can make up a large part of the bill. On a large one, they barely register.
Three places chargeable weight climbs
Switching from air to express
Take cargo with a density of 180 kg per cubic meter. By air, that’s above 166.67 kg/m³, so it’s billed on actual weight. By express, it’s below 200 kg/m³, so it’s billed on volumetric weight: 200 kg for every cubic meter instead of 180, about 11% more billed weight.
More billed kilograms don’t necessarily mean a higher bill. Each mode has its own per-kg rates, so compare costs only after confirming which divisor each quote applies.
Light, bulky cargo
Every mode has a density at which volumetric and actual weight are equal: about 167 kg/m³ (166.67) for air, 200 kg/m³ for express and 1,000 kg/m³ for ocean LCL. Cargo below that density is always billed on volume. The figure is the divisor turned around: 1,000,000 cm³ in a cubic meter divided by 6,000 gives 166.67 kg per m³.
Textiles, plastic parts and consumer goods in bulky packaging typically fall into this group. For them, cutting volume cuts chargeable weight directly: remove empty space, nest parts inside each other, use less filler and pick boxes that fit the product. If the shipment is already billed on actual weight, repacking for volume won’t change the chargeable weight. For more on repacking, see volumetric weight explained.
Reweighs and remeasures
Carriers can reweigh or remeasure a shipment, checking its weight and dimensions again on their own equipment. If their figures differ from what you declared, the bill can change and you can face extra charges you didn’t plan for. The best protection is to weigh and measure every package yourself before booking and keep a record of the results.
Work it out before you book
The chargeable weight calculator takes the dimensions, quantity and weight per box for each line. Choose one mode (air, express or ocean LCL) and it shows three results: actual weight, volumetric weight and chargeable weight. To compare modes, switch between them; the results show one mode at a time. If your carrier uses a different divisor, enter it as a custom divisor. For the volume calculation itself, see what CBM is and how to calculate it.
Why is my chargeable weight higher than the actual weight?
Because the shipment is light for the space it takes up. Carriers compare the actual weight with the volumetric weight worked out from the dimensions and bill whichever is higher. For air freight at a divisor of 6,000, anything under about 167 kg per cubic meter is billed on volume; for express at 5,000, the cut-off is 200 kg per cubic meter. Below those densities, the chargeable weight will always come out above the scale weight.
How do you calculate chargeable weight for air freight?
Measure each package at its longest, widest and highest points, including any bulges or overhang. Multiply length × width × height in centimeters and divide by 6,000 to get the volumetric weight in kilograms. Compare that with the actual gross weight and take the higher figure; airlines may round it up to the next 0.5 kg. Express services often divide by 5,000 instead, so check which divisor your quote uses.
What is the difference between chargeable weight and gross weight?
Gross weight is what the shipment weighs on a scale: the goods plus all packaging, and the pallet if it ships on one. Chargeable weight is the figure the freight charge is calculated on, which is the higher of the gross weight and the volumetric weight. When the gross weight is equal to or greater than the volumetric weight, the two are the same before rounding; otherwise the chargeable weight is higher.
Do all express carriers use a divisor of 5,000?
No single divisor applies across the board. UPS in the UK, for example, divides cm³ by 5,000. UPS in the US divides cubic inches by 139 or 166, depending on the rate type, and 139 in³/lb works out close to 5,000 cm³/kg. Divisors vary by carrier, service and country and can change, so confirm the figure in the carrier’s current service guide or in your quote.
Can chargeable weight be lower than the actual weight?
No. Chargeable weight is the higher of actual and volumetric weight, so it can equal the actual weight for dense cargo but never fall below it. The total charge can still go down, though: if charging the shipment as if it weighed the starting weight of the next weight break, at that break’s lower rate, comes out cheaper, airlines apply the lower charge.
Why was I billed for more weight than I declared?
Carriers can reweigh or remeasure a shipment, and if their figures differ from what you declared, the bill can change and extra charges can follow. Dimensions are taken at the extreme points of each package, so bulging boxes, overhang and irregular shapes all add volume, and carriers handle fractions of a centimeter or inch in different ways. Weighing and measuring every package yourself before booking, and keeping a record, is the best protection.
Is dimensional weight the same as chargeable weight?
No. Dimensional weight, dim weight and volume weight are other names for volumetric weight: the weight calculated from a shipment’s size. Chargeable weight, also called billed weight, is the final figure you pay on: the higher of the volumetric weight and the actual weight.