The Twenty-Foot Container is the 20-foot ISO general-purpose intermodal container, the smallest of the standard ocean shipping container sizes. Coded “20’GP” or “20’DC” (general-purpose / dry cargo) by carriers, the container has internal dimensions of approximately 5.9 m × 2.35 m × 2.39 m, payload capacity of 28 MT (28,000 kg), and volume capacity of approximately 33 cubic metres. The 20-foot container is the unit measure for container shipping statistics. TEU, the Twenty-foot Equivalent Unit, normalises capacity across the global container fleet. For chemical sourcing from China, the 20’GP is the standard for drum and IBC cargo at parcel scale.
Standard 20’GP dimensions and capacity
| Dimension | External | Internal |
|---|---|---|
| Length | 6.058 m (20 feet) | 5.898 m |
| Width | 2.438 m (8 feet) | 2.352 m |
| Height | 2.591 m (8 feet 6 inches) | 2.393 m |
| Door height | n/a | 2.275 m |
| Door width | n/a | 2.343 m |
| Maximum gross mass | 30,480 kg (international standard) | n/a |
| Tare mass | ~2,200-2,300 kg | n/a |
| Maximum payload | ~28,200 kg | n/a |
| Internal volume | n/a | ~33.2 m³ |
The internal door dimensions are slightly smaller than the internal cargo dimensions, pallets and IBCs that fit inside the container must enter through the door clearance. This is a recurring loading constraint.
Cargo capacity for chemical formats
| Cargo format | Capacity per 20’GP |
|---|---|
| 200-kg drums on pallets (4 drums per pallet) | 80 drums (~16 MT cargo + tare) |
| 220-kg drums on pallets (4 drums per pallet) | 80 drums (~17.6 MT cargo + tare) |
| 1,000-kg IBCs | 16-18 IBCs (~16-18 MT cargo + tare) |
| 1,000-kg big bags | 18-20 bags (~18-20 MT cargo + tare) |
| ISO tank | 1 tank (the tank is itself 20-foot ISO frame) |
| 25-kg multi-wall paper bags on pallets (40 bags per pallet) | 28 pallets (~28 MT cargo) |
The cargo-weight-vs-volume trade-off is the recurring loading question. Heavy cargoes (acids in steel drums) cube out at 16-18 MT well before filling the volume. Light cargoes (low-density powders in big bags) volume out before reaching the 28 MT weight limit.
The cube-out vs weight-out economics
For a 20’GP shipment of caustic soda solid in 25-kg paper bags:
- Cargo at SG ~2.1 (dense solid, but bagged at bulk density ~0.9-1.0 t/m³ accounting for bag voidage)
- Container fits 28 pallets × 40 bags = 1,120 bags = 28 MT
- The container is at weight maximum (~28 MT cargo) and at volume ~26 m³, slightly under volumetric capacity
- This is “weight out”, the container reaches maximum gross mass before volume
For a 20’GP shipment of low-density expanded polystyrene beads in big bags:
- Cargo at bulk density ~0.05 t/m³
- Container fits 18 big bags × ~33 m³ ÷ 18 ≈ 1.8 m³ per bag at 90 kg per bag = 1.6 MT total
- The container is at volume maximum (~33 m³) and at weight ~1.6 MT, far under weight limit
- This is “cube out”, the container reaches volume limit before weight
For routine chemical drum cargo, the typical loading is weight-out at 16-18 MT cargo per container.
Container weight regulations and SOLAS VGM
Since 2016, the IMO SOLAS amendment requires the verified gross mass (VGM) of every container be declared by the shipper before loading. The VGM is the sum of the cargo, packaging, and container tare. For a chemical shipment loading 16 MT cargo into a 2.2 MT tare 20’GP, the declared VGM is 18.2 MT. The carrier verifies this against weighbridge readings; mismatches can result in cargo rejection at the load port.
For chemical buyers, the implication is the cargo must not exceed the declared VGM minus the actual tare. A buyer ordering “20 MT in a 20-foot container” with the supplier declaring tare at 2.2 MT and cargo at 19.8 MT may find the loading post fewer bags or drums than the order called for if the actual loading would exceed the VGM commitment.
Hazmat surcharges on 20’GP
DG cargo in 20’GP attracts hazmat surcharges that vary by carrier and cargo class. Typical ranges:
| IMDG class | Hazmat surcharge per 20’GP container |
|---|---|
| Class 3 (flammable liquids) | USD 100-300 |
| Class 8 (corrosives) | USD 100-300 |
| Class 5.1 (oxidisers) | USD 200-500 |
| Class 6.1 (toxics) | USD 300-800 |
| Class 9 (lithium batteries specifically) | USD 400-1,200 |
The surcharges are often subject to volatility and carrier-specific differentiation. Always confirm at booking, not on standard rate cards.
When 20’GP is the right container
20’GP is the right choice for:
- Heavy chemical cargo (drums, IBCs of high-density liquids) where the 28 MT weight limit fills before the volume
- Mixed-cargo consolidations where pallet count fits 20’GP capacity
- Routes with limited 40’GP availability or 40’GP rate premiums
- First-time supplier qualification orders where smaller volumes match 20’GP capacity better than 40’GP
When 20’GP is the wrong container
20’GP is wrong for:
- Low-density bulk cargoes that cube out well below 28 MT, a 40’GP or 40’HC carries more for similar freight cost per box
- Volume buyers running 20+ MT per shipment of a single cargo where 40’GP / 40’HC volume capacity is better utilised
- ISO tank shipments, which use a dedicated 20-foot tank frame rather than a general-purpose container
Operator note: the 20’GP-vs-40’HC freight rate
Carrier freight rates for 20’GP vs 40’HC (40-foot High Cube) are typically 70-80% of the 40’HC rate. For weight-out cargo where 20’GP fills with the same cargo weight as 40’HC (because 20’GP and 40’HC share the same 28-30 MT weight cap), 40’HC is almost always cheaper per tonne. For volume-out cargo, the 20’GP can be cheaper per cubic metre. For mixed cargo, cube vs weight calculation determines the optimal container choice.
Related terms
Forty-foot container and Forty-foot High Cube are the larger sizes. IBC, drum, and big bag are the standard cargo formats fitting inside 20’GP. ISO tank uses the 20-foot ISO frame for bulk liquids.