For garment manufacturers and exporters in Bangladesh, shipping space is money. Whether you are exporting shirts, denims, or knitwear, freight pricing is determined either by cargo weight or volume. Under-utilizing a shipping container can cost thousands of dollars in wasted space, while overloading a container can lead to customs fines, shipping line rejections, or port accidents. This guide details how to calculate cargo volume (CBM), standard ocean container capacities, payload weight checks, and practical packing strategies to maximize container utilization.
What is CBM and How Do You Calculate It?
CBM stands for Cubic Meters. It is the international standard unit of measurement for shipping volume. To find the CBM of a single carton box, you multiply its length, width, and height in metres. Since most cartons are measured in centimetres, the formula is scaled by dividing by 1,000,000:
Single Carton CBM (Metric): CBM = (Length cm × Width cm × Height cm) ÷ 1,000,000 Example: A carton measuring 60 cm × 40 cm × 30 cm: CBM = (60 × 40 × 30) ÷ 1,000,000 = 72,000 ÷ 1,000,000 = 0.072 CBM Total Shipment CBM: Total CBM = CBM per carton × Total Carton Quantity For 500 cartons: 0.072 × 500 = 36.00 CBM
Note
If your buyers specify dimensions in inches (imperial), you can calculate CBM by multiplying the length, width, and height in inches, and then dividing by 61,023.74 (the number of cubic inches in a cubic meter). Total Cubic Feet (CFT) is calculated by multiplying CBM by 35.3147.
Standard Shipping Container Volumes & Payloads
Standard ocean containers have maximum theoretical volumes and gross payload weight limits defined by ISO standards. However, because boxes are rectangular and have manual packing constraints, you can rarely pack a container to 100% of its theoretical volume. The table below lists standard container sizes, their theoretical limits, and their realistic usable capacities.
Ocean Shipping Container Specifications & Usable Volume
| Container Type | Max Volume (Theoretical) | Usable Volume (Realistic) | Max Payload Weight | Best Suited For |
|---|---|---|---|---|
| 20' Standard (20GP) | 33.2 CBM | 28 – 30 CBM | 21,800 kg (21.8t) | Heavy goods: denims, bulk yarns, machinery |
| 40' Standard (40GP) | 67.7 CBM | 58 – 62 CBM | 26,700 kg (26.7t) | General light cargo, carton boxes, knitwear |
| 40' High Cube (40HC) | 76.4 CBM | 68 – 72 CBM | 26,500 kg (26.5t) | Volumetric cargo, hung garments, tall packages |
| 45' High Cube (45HC) | 86.0 CBM | 78 – 82 CBM | 25,600 kg (25.6t) | Lightweight, high-volume shipping |
The Volumetric Weight vs. Physical Weight Rule
Shipping lines charge based on the greater of two values: physical weight or volumetric weight. This is particularly important for air cargo and courier express shipments. Volumetric weight is calculated using the following industry standard formula:
Volumetric Weight (kg) = (Length cm × Width cm × Height cm) ÷ 5,000 Example for 1 carton (60 × 40 × 30 cm, 12 kg physical weight): Volumetric weight = (60 × 40 × 30) ÷ 5,000 = 72,000 ÷ 5,000 = 14.4 kg Since 14.4 kg (volumetric) > 12.0 kg (physical), the courier will bill you for 14.4 kg. If shipping 500 cartons, the billable weight difference is 1,200 kg!
How to Optimize Container Loading
- Check Carton Bulging: Overstuffed cartons bulge at the sides, increasing their effective shipping size. Allow a 3-5% margin on carton dimensions when planning loading layouts.
- Weight vs Volume Limits: Always multiply carton gross weight by quantity. If total weight exceeds the container's payload limit (e.g. 21.8 tonnes for 20ft), you must split the shipment, even if the container volume is only half-filled.
- Staggered Packing Layout: Stagger the packing layers (similar to bricklaying) to prevent columns from tipping and fill gaps caused by corner posts and door hinges.
- Palletisation Loss: If cargo is palletised rather than hand-loaded, you will lose up to 10% more volume due to pallet dimensions and spacing requirements.
Tip
Use the CostNest CBM & Container Loading Calculator to enter your carton dimensions, gross weights, and quantities. It estimates total CBM, total weight, volumetric weight, and provides realistic carton fits and volume/weight capacity utilization charts for standard shipping containers.