CBM Calculator

What is CBM and why does it determine your freight cost?

CBM (cubic metre) is the standard unit of measurement for shipping volume. Multiply length × width × height in metres. Freight carriers use CBM to determine how much space cargo occupies in a container, truck, or aircraft, and it directly determines what you pay for LCL (less-than-container load) shipments, where you are charged per cubic metre.

For FCL (full container load) shipments, CBM determines whether the container is worth booking. An LCL rate of AU$70 per CBM on a 25 CBM shipment costs AU$1,750. A 20ft FCL on the same route might cost AU$2,400. The FCL is more expensive in total but cheaper per CBM (AU$72.50 versus AU$70) only if you actually use the full 33 CBM. Below about 22-24 CBM, LCL wins on cost. Above that, FCL wins. The break-even point depends on the route and carrier, but the calculation always starts with knowing your CBM accurately.

How volume weight works

Volume weight (also called dimensional weight or volumetric weight) converts the physical size of a shipment into a weight equivalent. Carriers use it to charge fairly for lightweight but bulky items that take up space without contributing much actual weight.

The conversion factors differ by transport mode:

• Sea freight: 1 CBM = 1,000 kg (1 revenue tonne)
• Air freight (IATA standard): 1 CBM = 167 kg
• Air freight (some carriers): 1 CBM = 200-250 kg
• Road freight (Australian domestic): varies by carrier, typically 1 CBM = 250-333 kg

The chargeable weight is whichever is greater: actual weight or volume weight. A shipment of 10 CBM of pillows weighing 200 kg has a volume weight of 1,670 kg for air freight. The carrier charges based on 1,670 kg, not 200 kg. Missing this distinction when quoting freight costs to customers or estimating landed cost leads to margin surprises.

Worked examples

Single product shipment

A Melbourne retailer orders 300 cartons of homewares from a Guangzhou supplier. Each carton measures 50 × 40 × 30 cm and weighs 6 kg.

• Volume per carton: 0.50 × 0.40 × 0.30 = 0.06 CBM
• Total volume: 300 × 0.06 = 18 CBM
• Total weight: 300 × 6 = 1,800 kg
• Volume weight (sea): 18 × 1,000 = 18,000 kg

Actual weight (1,800 kg) is well below volume weight (18,000 kg). This shipment is volume-limited. The carrier charges based on CBM, not weight. At an LCL rate of AU$65/CBM, the freight cost is AU$1,170. A 20ft container (33.1 CBM) at AU$2,600 would be overkill at only 54% fill rate.

Mixed product shipment

A Brisbane wholesale distributor ships two product lines from the same supplier:

• Product A: 150 cartons at 60 × 45 × 40 cm, 14 kg each = 16.2 CBM, 2,100 kg
• Product B: 80 cartons at 30 × 30 × 25 cm, 18 kg each = 1.8 CBM, 1,440 kg

Total: 18 CBM, 3,540 kg. Product A is volume-heavy but light. Product B is dense but compact. Combined, the shipment fits in an LCL booking or justifies a 20ft container if additional stock can fill the remaining 15 CBM. Use the container load calculator to check whether the weight and volume both fit within the container limits.

Common CBM calculation mistakes

Measuring inner carton dimensions instead of outer. Carriers measure the outermost surface of each package. If your carton is 60 cm wide on the inside but 62 cm including the corrugated walls, 200 cartons adds up to 4 extra cm per carton. Over a full shipment, this means the actual CBM is higher than your estimate, and the LCL invoice will be higher than expected.

Not accounting for irregular shapes. Carriers charge on the rectangular bounding box, not the product shape. A 1-metre-diameter cylinder in a crate is charged as a 1 × 1 × height rectangle. The wasted space within the bounding box is still your cost.

Ignoring pallet overhang and height. If cartons are palletised, the CBM calculation needs to include the pallet (1,165 × 1,165 × 150 mm for a standard Australian pallet) and any overhang. A pallet load stacked 1.5 m high has a total height of 1.65 m including the pallet itself.

CBM and freight invoice verification

LCL freight invoices show the chargeable CBM alongside the rate per CBM. If the CBM figure on the carrier's invoice does not match your own calculation, the invoice amount is wrong. This happens regularly when the carrier measures at the warehouse and the shipper measured from product specs. A 10% CBM discrepancy on a 20 CBM shipment at AU$70/CBM is AU$140 per shipment. Across 15 LCL shipments per year, that is AU$2,100 in unverified overcharges.

Your AP team should cross-check the CBM figure on every LCL invoice against the shipping documentation. For businesses processing multiple freight invoices weekly, freight invoice reconciliation automation catches these discrepancies before payment, not after. See also handling carrier invoice discrepancies for the full AP workflow.

How to use this CBM calculator

1. Select your measurement unit (cm, m, or inches).
2. Enter dimensions for a single item, or switch to multi-item mode for mixed shipments with different carton sizes.
3. Enter the actual weight to compare against volume weight and determine the chargeable weight.
4. Review container fill percentages to decide between FCL and LCL shipping.

Frequently asked questions

How do you calculate CBM for shipping?

Multiply length × width × height in metres. For a carton measuring 60 cm × 40 cm × 35 cm: convert to metres (0.60 × 0.40 × 0.35) = 0.084 CBM per carton. Multiply by the number of cartons for total shipment volume. If your measurements are in centimetres, divide the final result by 1,000,000.

What is the difference between actual weight and volume weight?

Actual weight is what the shipment weighs on a scale. Volume weight converts the physical size into a weight equivalent using a carrier-specific factor. For sea freight, 1 CBM equals 1,000 kg. For air freight, 1 CBM equals 167 kg (IATA standard). The chargeable weight is whichever is greater.

How many CBM fit in a 20ft and 40ft container?

A 20ft standard container has approximately 33.1 CBM of usable volume. A 40ft standard container offers roughly 67.5 CBM. A 40ft high cube provides about 76.2 CBM due to the extra 30 cm of height. Actual usable volume is slightly less after accounting for pallets, load securing, and door opening restrictions.

When is a shipment volume-limited versus weight-limited?

Volume-limited means the cargo fills the container's space before reaching its weight limit. Common with furniture, clothing, and packaged goods. Weight-limited means the weight capacity is hit before the container is full. Common with tiles, steel, and canned goods. Knowing which constraint applies determines whether you optimise for packing density or weight distribution.