Free tool
Carton CBM calculator
Give a carton's outside dimensions and how many you are shipping. This works out the CBM, the cubic feet, and the volumetric weight air freight will charge.
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In short
- CBM in inches = length × width × height ÷ 61,024. In centimetres, divide by 1,000,000.
- Use the carton's OUTSIDE dimensions — freight pays for the space the carton takes, board and all.
- Multiply by the number of cartons for the shipment. 1 CBM is 35.3 cubic feet.
- Sea freight in a shared container is charged per CBM or per 1,000 kg, whichever is greater.
- Air freight uses volumetric weight: cm³ ÷ 6,000, or ÷ 5,000 for express couriers.
Work out the CBM
Measure the carton on the outside, at its longest, widest and tallest points. If the cartons are not made yet, the outside is the internal size plus the thickness of the board on both sides — the flute thicknesses give the idea. Ask your carton maker for the external size before you book freight.
Total CBM
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- One carton
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- Cubic feet, total
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- 20ft container, by volume
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- Shared container charged on
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- Air volumetric weight, per carton
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For your forwarder:
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Request a quoteThe formula
CBM is cubic metres — the volume a carton takes up, and the unit sea freight is priced in. There are three ways to reach it, depending on what your tape measures in:
A worked example, in inches
A shipment of 100 cartons, each 18 × 12 × 10 inches on the outside:
- One carton — 18 × 12 × 10 = 2,160 cubic inches
- In CBM — 2,160 ÷ 61,024 = 0.0354 CBM
- The shipment — 0.0354 × 100 = 3.54 CBM
- In cubic feet — 2,160 ÷ 1,728 = 1.25 per carton, 125 cubic feet in all
Outside for freight, inside for the order
This catches people in both directions. Freight is charged on the outsideof the carton, because that is the space it takes in the truck or the container, board and all. A carton is ordered by its inside, because that is the space the product needs — see how to measure a carton.
So the same carton has two sizes on two documents: the internal size on the purchase order to the carton maker, and the external size on the packing list to the forwarder. The gap between them is the thickness of the board on both sides, and it grows with the ply.
How many cartons fit in a container
Divide the container's usable volume by the CBM of one carton. The internal volumes below are the published figures for standard dry containers; the usable figure is lower, because cartons never tile a container perfectly and space is needed to load it.
| Container | Internal volume | Typically usable |
|---|---|---|
| 20ft | about 33 CBM | about 25–28 CBM |
| 40ft | about 67.7 CBM | roughly 80–90% of that |
| 40ft high cube | about 76.3 CBM | roughly 80–90% of that |
With the example cartons at 0.0354 CBM, a 20ft container takes roughly 700 to 790 by volume. That is a planning number: the weight limit, the way the cartons stack and whether they are palletised can all bring it down. Your forwarder's load plan is the real answer.
How sea freight is charged: W/M
If your goods share a container with other shippers — LCL, less than container load — you are charged per revenue ton: one CBM or 1,000 kg, whichever is greater. Quotes write it as W/M, weight or measure.
Cartons are almost always charged on volume. The example shipment of 3.54 CBM would have to weigh more than 3,540 kg — over 35 kg a carton — before weight took over.
How air freight is charged: volumetric weight
Air freight charges the greater of the actual weight and the volumetric weight — the size of the carton converted to kilograms, so a light, bulky carton pays for the space it takes on the aircraft.
The example carton of 2,160 cubic inches comes to about 5.9 kg by air freight and 7.1 kg by express courier, whatever it actually weighs. Confirm the divisor with your own carrier — it is set by the contract, not by law.
Paying for less air
Every inch of empty space inside a carton is paid for on every carton in the shipment. The direct way to lower the CBM is a carton cut to the product, and a master carton sized around its inner boxes rather than a stock size that nearly fits. The box size calculator works out the internal size from the product, and how many pieces fit in a carton covers choosing the count.
Common questions
What is the formula for carton CBM in inches?
Multiply length × width × height in inches, then divide by 61,024. A carton of 18 × 12 × 10 inches is 2,160 cubic inches, which is 0.0354 CBM. Multiply by the number of cartons for the total. The 61,024 comes from 1 cubic metre being 39.37 inches on each side.
What is the formula for carton CBM in centimetres?
Multiply length × width × height in centimetres and divide by 1,000,000. A carton of 46 × 30 × 25 cm is 34,500 cubic centimetres, which is 0.0345 CBM. In metres it is simpler still: 0.46 × 0.30 × 0.25 = 0.0345 CBM.
Should CBM use the internal or external size of the carton?
External. Freight is charged on the space the carton takes up in a container or a truck, and that is its outside size, including the thickness of the board. This is the opposite of how a carton is ordered — you give a manufacturer internal dimensions, because that is the space your product needs.
How many cartons fit in a 20ft container?
Divide the usable volume by the CBM of one carton. A 20ft container is about 33 CBM inside, but gaps between cartons and the space needed to load mean roughly 25 to 28 CBM is usable in practice. So cartons of 0.0354 CBM fit roughly 700 to 790 by volume alone. Weight limits, the carton sizes and how they stack can bring the real number down — your forwarder or a load plan gives the exact figure.
How is air freight charged — by weight or by CBM?
By chargeable weight, which is the greater of the actual weight and the volumetric weight. Volumetric weight is the carton's size in cubic centimetres divided by 6,000 for most air freight, or by 5,000 for express couriers. In inches, divide cubic inches by 366 or by 305. A light but bulky carton is therefore charged as if it were heavier.
How do I reduce the CBM of a shipment?
Make the carton fit the product. Every inch of empty space in a carton is paid for on every carton in the shipment, so a carton sized to the product — and a master carton sized to the inner boxes — is the direct way down. Printing the carton does not change its CBM; its size does.
