Shipping Container Sizes, Types and Capacities Explained

Shipping container dimensions and payloads: 20' and 40' dry, 40' high cube, reefer, open top and flat rack, with pallet counts, VGM rules and a loading example.

Containers carry most of the world's manufactured goods, and choosing the right one is a decision exporters make on almost every sea shipment. The wrong box means paying for space you do not use, leaving cargo behind at the quay, exceeding a road weight limit, or damaging goods that needed temperature control or top loading.

This lesson gives you the real working figures for the main container types: internal dimensions, door openings, tare, payload and volume. It shows how many pallets fit, how to decide whether your cargo is limited by weight or by volume, which specialised containers exist, and what the SOLAS verified gross mass (VGM) rule requires from you as shipper.

All figures below are typical values. Dimensions, tare and payload vary by shipping line, manufacturer and container series, so always check the line's equipment page and the markings on the container itself.

How are containers measured: TEU, FEU and ISO sizes

Containers are standardised under ISO 668. External dimensions are 8 feet (2.438 m) wide, 20 or 40 feet long (6.058 m or 12.192 m) and 8'6" (2.591 m) high for a standard box or 9'6" (2.896 m) for a high cube.

Capacity and ship sizes are counted in TEU (twenty-foot equivalent unit): a 20' container is 1 TEU, a 40' is 2 TEU (sometimes called an FEU). A vessel of 15,000 TEU can carry 15,000 twenty-foot boxes or 7,500 forty-foot boxes, in theory.

Every container carries a unique number under ISO 6346, for example MSCU 123456 7: a three-letter owner code, the category letter U for freight containers, a six-digit serial number and a check digit. This is the number on your bill of lading and the one you use for tracking. Each box also bears a CSC safety approval plate showing its maximum gross mass and tare.

Standard dry containers: dimensions and payloads

Note the paradox: a 40' does not carry twice the weight of a 20'. Most dry containers have a maximum gross mass of 30,480 kg or 32,500 kg, so the 40' payload is similar to, or only slightly above, the 20' payload. Heavy goods go in 20' boxes; light, bulky goods go in 40' high cubes.

Usable volume is always lower than the nominal volume. Allow for pallet gaps, door clearance and securing, and plan for about 85 to 90% of the nominal cubic capacity with well-palletised cargo.

How many pallets fit in a container?

Double stacking doubles these numbers only if the lower pallets can bear the weight of the upper ones and the total stack fits under the door height (2.28 m in a standard box, about 2.58 m in a high cube).

Specialised containers

Reefer containers

A reefer container has an integrated refrigeration unit and insulated walls, and holds a set temperature typically between about −30 °C and +30 °C. Insulation makes it narrower and shorter inside than a dry box:

The cargo must stay below the red load line painted on the side walls, which reduces usable volume to about 65 m³ in a 40' HC reefer. Reefer operation is covered in shipping perishables.

Open top, flat rack and others

• Open top (20' or 40'): no fixed roof, a removable tarpaulin and often a removable door header, so cargo can be crane-loaded from above. Internal height about 2.35 m; 20' payload about 28 tonnes, 40' about 26.5 tonnes. Used for machinery, marble blocks, glass, tall crates. Cargo may stick out above the roof, at an out-of-gauge surcharge.
• Flat rack (20' or 40'): a floor with end walls, often collapsible, and no sides or roof. Takes over-width and over-height cargo such as vehicles, transformers, boats and steel structures. A 40' flat rack typically has a payload of 39 to 40 tonnes (maximum gross mass about 45 tonnes); a 20' about 27 to 31 tonnes. Out-of-gauge cargo pays a premium and is stowed where no box sits on top of it, so book early.
• Hard top: a steel roof that can be lifted off, for heavy cargo loaded from above.
• Ventilated: for cargo such as coffee or cocoa beans that must breathe.
• Tank container (ISO tank): a stainless tank in a 20' frame for liquids, food-grade or chemical, typically 14,000 to 26,000 litres.
• Flexitank: a single-use bladder of up to about 24,000 litres installed in a 20' dry box, for non-hazardous liquids such as wine, edible oils or juice concentrate.

Is your cargo limited by weight or by volume?

Divide the container's payload by its usable volume to get its break-even density:

• 20' dry: about 28,000 kg ÷ 30 m³ ≈ 930 kg per m³
• 40' high cube: about 26,500 kg ÷ 68 m³ ≈ 390 kg per m³

If your packed cargo (with pallets) is denser than that, you will hit the weight limit first; if it is lighter, you will run out of space first. Compute your cargo's density from the packing list: total gross weight divided by total volume.

What is VGM and how do you declare it?

Since 1 July 2016, Chapter VI, Regulation 2 of the SOLAS Convention requires the verified gross mass (VGM) of every packed export container to be provided before it can be loaded on a ship. A container without a VGM is not loaded.

The shipper named on the bill of lading is responsible for the VGM and must determine it by one of two methods:

1. Method 1: weigh the packed and sealed container on calibrated, certified equipment such as a weighbridge.
2. Method 2: weigh all packages and cargo items, add the mass of pallets, dunnage, packing and securing material, then add the container's tare written on its door. The method must be approved or recognised by the competent authority of the country where packing takes place, and is not appropriate for some loose bulk cargo.

The VGM is signed by a person authorised by the shipper and sent to the carrier or terminal (usually electronically through the forwarder) before the VGM cut-off given in the booking. National authorities set the tolerance between declared and actual weight and the penalties, so ask your forwarder about local practice.

How to choose and check a container

1. Calculate gross weight, volume and density from the packing list.
2. Choose the type (dry, high cube, reefer, open top, flat rack) and size that meets both limits.
3. Check the inland weight limit with your haulier.
4. Specify in the booking any requirement: food-grade, clean and odour-free, new or nearly new box.
5. Inspect the empty container on arrival: CSC plate valid, no holes (close the doors from inside and look for light), dry clean floor, working door seals, no old dangerous goods labels, no smell.
6. Load evenly along the length, heaviest at the bottom, centre of gravity near the middle, and secure the load against movement, following the IMO/ILO/UNECE CTU Code.
7. Record the container and seal numbers and the VGM; they go on the bill of lading and in the packaging and marking records.

Common mistakes with containers

• Booking a 40' for heavy cargo and expecting twice the payload of a 20'.
• Planning on the nominal volume instead of the usable volume.
• Forgetting the load line in a reefer, or the reduced inside width of a reefer when planning pallets.
• Declaring a VGM that ignores pallets, dunnage or the tare.
• Accepting an empty box without inspecting it, then discovering water damage at destination.

Once you know which box you need, the next question is whether you need a whole one: that is the FCL vs LCL decision.