CBM Calculator for Shipping
Enter the length, width, height, and weight of your carton and the number of cartons to get the total CBM (cubic meters), volumetric weight, chargeable weight, and estimated container fill percentage for standard shipping containers. Switch between centimetres and inches. Results update as you type.
What is CBM and why it matters for shipping
CBM stands for cubic metre, the standard unit used in international freight to measure how much space a shipment occupies. Shipping lines, freight forwarders, and logistics providers use CBM to price sea freight under the weight-measurement (W/M) rule: you pay whichever is greater between actual weight (in metric tons) and volume (in cubic metres). Knowing your CBM before you book lets you avoid costly surprises at the origin port and gives you a concrete figure to compare quotes from different carriers. CBM is calculated by multiplying the external length, width, and height of each carton, then multiplying by the quantity of cartons. The result is the gross volume of the cargo before any packing efficiency is applied. Because boxes rarely stack perfectly, shippers typically allow an efficiency factor of 85-90% when working out how many cartons will physically fit in a container.
Volumetric weight and chargeable weight explained
Air couriers and many road carriers charge on dimensional (volumetric) weight rather than actual weight when the cargo is bulky but light. Volumetric weight is calculated by dividing the carton volume in cm3 by a carrier-specific divisor: 6,000 is standard for air couriers such as DHL and FedEx, 5,000 is used by some sea and air carriers, and 4,000 appears in some road freight tariffs. A divisor of 6,000 means one cubic metre (1,000,000 cm3) equates to roughly 167 kg of volumetric weight. Chargeable weight is simply the higher of actual weight and volumetric weight. If your 100 cartons weigh 500 kg but have a volumetric weight of 750 kg, you will be billed as if the shipment weighs 750 kg. Knowing this in advance lets you either repack cartons to reduce dead space or adjust your freight budget accordingly.
Choosing and filling a shipping container
The four most common dry containers in ocean freight are the 20 ft standard (one TEU), the 40 ft standard (one FEU), the 40 ft high cube, and the 45 ft high cube. The 40 ft high cube has an extra 30 cm of internal height compared with the standard 40 ft box, which is valuable for tall or irregularly shaped cargo. The 45 ft high cube is common on intra-European rail and road routes but less so on deep-sea services. Practical usable capacity is always lower than the nominal internal volume shown in container specifications. A 20 ft standard has a nominal volume of about 33 m3 but you can reliably load only around 25 CBM of rectangular cartons. For LCL (less-than-container-load) shipments, where your cargo shares space with other shippers, you pay per CBM. For FCL (full-container-load), maximising fill reduces cost per unit.
How to reduce your shipping cost per unit
There are three practical levers. First, reduce carton size: even a small reduction in each dimension compounds quickly across thousands of cartons and can tip a two-container order into one. Second, increase carton density: if volumetric weight exceeds actual weight, adding weight (denser packing, less void fill) up to the point where actual weight matches volumetric weight will not increase your freight cost at all. Third, compare container sizes: a 40 ft high cube often costs only 10-15% more than a 20 ft but holds more than twice the volume, so the cost per CBM drops sharply when you can fill it.
Standard shipping container usable capacities
| Container type | Nominal internal volume | Practical usable CBM | Typical max weight |
|---|---|---|---|
| 20 ft standard (TEU) | 33.2 m3 | ~25 CBM | 28,000 kg |
| 40 ft standard (FEU) | 67.6 m3 | ~55 CBM | 26,000 kg |
| 40 ft high cube | 76.3 m3 | ~63 CBM | 26,500 kg |
| 45 ft high cube | 86.0 m3 | ~72 CBM | 27,600 kg |
Practical usable volumes allow for irregular stacking and dunnage. Nominal internal volumes are higher.
Frequently asked questions
What does CBM mean in shipping?
CBM stands for cubic metre (m3), the standard volume unit used to measure cargo in international freight. Shipping lines and freight forwarders use it to price sea freight and to work out how many shipments can fit in a container. It is calculated by multiplying the length, width, and height of each carton in metres, then summing across all cartons.
How do I calculate CBM?
Multiply the external length, width, and height of one carton (all in metres), then multiply by the number of cartons. For example, a carton that is 0.60 m long, 0.40 m wide, and 0.30 m high has a volume of 0.60 x 0.40 x 0.30 = 0.072 m3. One hundred of those cartons would be 7.2 CBM. If your measurements are in centimetres, multiply L x W x H and divide by 1,000,000.
What is the difference between CBM and volumetric weight?
CBM is a pure volume measurement in cubic metres. Volumetric weight converts that volume into a fictitious weight using a divisor set by the carrier: divide the carton volume in cm3 by 6,000 for most air couriers, 5,000 for some sea/air carriers, or 4,000 for some road carriers. This is used when bulky light cargo would cost less than dense heavy cargo to transport; the carrier charges on whichever is higher.
How many CBM fit in a 20 ft container?
A 20 ft standard dry container has a nominal internal volume of about 33.2 m3, but practical loading capacity for rectangular cartons is around 25 CBM once you allow for stacking inefficiency and dunnage. A 40 ft standard holds around 55 CBM practically, and a 40 ft high cube around 63 CBM.
What divisor should I use for volumetric weight?
Use 6,000 for air express couriers (DHL, FedEx, UPS, TNT). Use 5,000 for sea-air or some consolidation carriers. Use 4,000 for some European road freight tariffs. Always confirm with your specific carrier as divisors can vary by service level and trade lane. For pure ocean LCL freight the W/M rule applies (1 CBM = 1 revenue tonne = 1,000 kg), so the concept of a divisor does not directly apply.
Should I book LCL or FCL?
LCL (less-than-container-load) is usually cost-effective for shipments under about 15 CBM on most trade lanes. Above that threshold, booking an FCL 20 ft container is typically cheaper per CBM and gives you more control over handling and transit time. At around 25-28 CBM you are approaching a full 20 ft container, so comparing FCL 20 ft rates against LCL rates is worthwhile.
Why is my container fill percentage important?
Container fill percentage tells you how efficiently you are using the space you are paying for. Under 50% fill on an FCL booking means you are paying for a lot of air. Over 85-90% fill is a good target for FCL shipments. If your fill exceeds 100%, you need at least one additional container. The calculator uses practical usable volumes rather than nominal internal volumes for a realistic estimate.