About this calculator
Choosing between one 40 ft container and two 20 ft containers is not only a question of volume. A 40' GP offers roughly twice the space of a 20' GP, but its payload is actually slightly lower, and a 40' rate is usually not twice a 20' rate. As a result, light and bulky cargo is almost always cheaper in a 40' or 40' HC, while dense cargo such as tiles, steel or paper reels often makes more sense in several 20' boxes.
This calculator works out the units needed for each type in two ways: by volume (cargo volume divided by internal volume times a load factor, 85% by default) and by weight (cargo weight divided by payload). The number of units is the larger of the two. It then searches for the best combination across types: if you enter a rate per container it picks the lowest total cost; otherwise it picks the fewest TEU, then the fewest units, then the highest utilisation.
The 85% load factor stands for space lost to gaps and stacking limits in a typical mixed carton load; lower it for irregular goods, raise it for uniform cartons you have already counted. The result is an aggregate estimate, not a real stowage pattern. Rates you enter are not stored and are not official tariffs; get a quotation from your forwarder or carrier, then check the arrangement in the 3D Planner.
Worked example
A load of 50 m³ weighing 12 tonnes, load factor 85%:
- Usable volume per unit: 20' GP 28.2 m³, 40' GP 57.6 m³, 40' HC 64.9 m³
- Units needed: 20' GP 2, 40' GP 1, 40' HC 1 (12 t fits in every type)
- Without rates: every option is 2 TEU; 2 × 20' loses because it needs 2 units, and between the 40' GP and 40' HC (1 unit each) the 40' GP wins on higher utilisation (50 ÷ 67.7 ≈ 74% vs 50 ÷ 76.4 ≈ 65%)
- With rates of 1,000 / 1,500 / 1,600: 2 × 20' = 2,000, 40' GP = 1,500, 40' HC = 1,600
Result: book one 40' GP, at about 30 per m³ against 40 per m³ for two 20' boxes.
How to use it
Enter volume and weight
Fill in the total cargo volume in m³ and total weight in kg. Use the CBM calculator if you do not know the volume yet.
Set the load factor
Keep 85% for an ordinary carton load, or change it based on your experience with this kind of cargo.
Add rates if you have them
Enter an all-in rate per container for 20', 40' and 40' HC in the same currency so the calculator can pick the cheapest mix.
Compare and plan
See units, volume and weight utilisation, cost per m³ and the best combination, then open the chosen container in the 3D Planner.