# CBM meaning and how to calculate it

CBM means cubic metre, the unit of volume used in shipping. It is length × width × height in metres, multiplied by the number of cartons. A 50 × 40 × 30 cm carton is 0.5 × 0.4 × 0.3 = 0.06 m³, so 120 of them are 7.2 m³.

## Key takeaways

- Convert every dimension to metres before you multiply.
- Total CBM = CBM per carton × number of cartons; add each carton size separately for a mixed shipment.
- A 20GP holds about 33.2 m³ and a 40HQ about 76.4 m³ in theory; real loads fit less.
- Sea LCL is charged on the larger of cubic metres and metric tons (weight or measure).

## What CBM means

CBM stands for cubic metre, the unit forwarders, shipping lines and warehouses use to describe how much space a shipment takes. One cubic metre is a cube 1 m long, 1 m wide and 1 m high. A quote for sea freight, a container booking or a warehouse storage fee usually starts from the CBM of the goods.


## The formula

Measure the outside of one packed carton, convert to metres, multiply, then multiply by the number of cartons:

> **CBM = length (m) × width (m) × height (m) × number of cartons**

Dimensions are usually written in centimetres, so divide each one by 100 first. If you prefer to keep centimetres, multiply them and divide by 1,000,000 (because 100 × 100 × 100 cm³ = 1 m³).


### Example: one carton size

| Step | Working | Result |
|---|---|---|
| Carton size | 50 × 40 × 30 cm | 0.50 × 0.40 × 0.30 m |
| CBM per carton | 0.50 × 0.40 × 0.30 | 0.06 m³ |
| 120 cartons | 0.06 × 120 | 7.2 m³ |
| In cubic feet | 7.2 × 35.3147 | 254.3 ft³ |


[Check it in the CBM calculator](https://cartonmath.com/cbm-calculator/?unit=cm&l=50&w=40&h=30&qty=120): Opens with 120 cartons of 50 × 40 × 30 cm.


## CBM for a mixed shipment

Most export orders contain more than one carton size. Work out the CBM of each line, then add them up. The weight is added the same way.

| Carton (cm) | Qty | CBM per carton | Line CBM | Line weight |
|---|---|---|---|---|
| 60 × 40 × 40 | 50 | 0.096 | 4.8 | 900 kg |
| 40 × 30 × 20 | 120 | 0.024 | 2.88 | 1,080 kg |
| 80 × 60 × 50 | 10 | 0.24 | 2.4 | 300 kg |
| Total | 180 |  | 10.08 m³ | 2,280 kg |


[Load this shipment in the CBM calculator](https://cartonmath.com/cbm-calculator/?unit=cm&rows=60x40x40x50x18,40x30x20x120x9,80x60x50x10x30): All three lines prefilled, with the totals and container fill.


## How CBM relates to container size

Container capacity is often quoted in cubic metres. These are the typical internal dimensions of standard dry containers and the volume they give:

| Container | Inside L × W × H (mm) | Volume (m³) | Typical payload (kg) |
|---|---|---|---|
| 20GP | 5,898 × 2,352 × 2,393 | 33.2 | 28,000 |
| 40GP | 12,032 × 2,352 × 2,393 | 67.7 | 26,700 |
| 40HQ | 12,032 × 2,352 × 2,698 | 76.4 | 26,500 |
| 45HQ | 13,556 × 2,352 × 2,698 | 86 | 25,600 |


The 10.08 m³ shipment above would use about 30 % of a 20GP's theoretical volume. In practice you cannot fill every gap: cartons rarely divide the inside dimensions exactly, and pallets, door clearance and securing all take space. Planning for roughly 80–90 % of the theoretical volume is a common rule of thumb, and the [container loading calculator](https://cartonmath.com/container-loading-calculator/) shows the real fit for a given carton size.


## CBM and freight charges


### Sea LCL: weight or measure

Less-than-container-load (LCL) sea freight is usually charged per revenue ton: the larger of the volume in cubic metres and the weight in metric tons. The mixed shipment is 10.08 m³ and 2.28 t, so it is charged as 10.08 revenue tons.


### Air freight: volumetric weight

Airlines compare actual weight with a volumetric weight, commonly at 1:6000 (166.67 kg per m³). The same 10.08 m³ would count as 1,680 kg by volume against 2,280 kg actual, so it would be charged on the actual weight. Read more in [air freight chargeable weight](https://cartonmath.com/guides/air-freight-chargeable-weight/).


## Common mistakes

- Measuring the product instead of the packed carton. Use the outside of the shipping carton, including bulges.
- Mixing units: one dimension in millimetres and two in centimetres gives a figure 10 times too large or small.
- Rounding each carton's CBM to one decimal before multiplying by hundreds of cartons. Keep three decimals per carton.
- Forgetting pallets. A palletised shipment's CBM is the pallet footprint × the loaded height, not the sum of the cartons.

## FAQ

**What is CBM in shipping?**
CBM stands for cubic metre (m³). Forwarders, shipping lines and warehouses use it to measure how much space cargo takes, to choose a container and to price LCL sea freight.

**How do I calculate CBM in centimetres?**
Multiply length × width × height in centimetres and divide by 1,000,000. For example 50 × 40 × 30 = 60,000 cm³ = 0.06 m³.

**How many cubic feet are in one CBM?**
One cubic metre is 35.3147 cubic feet.

**How many CBM fit in a 20 ft container?**
A standard 20GP has about 33.2 m³ of internal volume. Real cargo usually fits around 80–90 % of that, depending on the carton size.

**How is LCL freight charged?**
Usually per revenue ton: the larger of the cubic metres and the metric tons of the shipment, with a minimum charge set by the forwarder.

Source page: https://cartonmath.com/guides/how-to-calculate-cbm/
Updated: 2026-10-06
Publisher: CartonMath (https://cartonmath.com)