To choose the right shipping container for your cargo, you need three facts before you ask anyone for a quote: how much space the packed cargo takes, how much it weighs, and how long, wide and tall its largest piece is. Most container mistakes come from guessing one of those three. A container that is big enough by volume can still be too light for dense cargo, and one with plenty of payload can still be too low for a tall crate. This guide gives you a six-step method, reference sizes from two carriers, three worked examples with made-up cargo and a list of mistakes to avoid.
If you are still deciding between a whole container and a shared one, read FCL vs LCL shipping first. For a closer look at the size differences, see 20ft vs 40ft shipping containers.
The Main Container Choices
| Container | Best suited to | Check first |
|---|---|---|
| 20ft dry | Dense or heavy cargo, smaller volumes | Weight against payload, volume against capacity |
| 40ft dry | Large volumes of general cargo | Payload, because it is not double that of a 20ft |
| 40ft high cube | Light, bulky or tall cargo | Door height and the height of your tallest item |
| Reefer | Goods that need a controlled temperature | Temperature range and power arrangements, and less space than a dry box |
| Open top | Cargo loaded from above or taller than the door | How it will be lifted in and how it will be covered |
| Flat rack | Heavy or oversized cargo that does not fit a closed box | Securing method and whether over-dimension charges apply |
Our guide to container types explains each type. This article is about choosing between them.
Reference Sizes From Two Carriers
The figures below are published carrier specifications. ONE's dry container table says it is for reference only and that individual containers may differ. The reefer figures come from Maersk's reefer specification sheet.
| Container | Internal length x width x height | Capacity | Payload |
|---|---|---|---|
| 20ft dry (ONE) | 5,898 x 2,350 x 2,390 mm | 33.1 m3 | 28,330 kg |
| 40ft dry (ONE) | 12,032 x 2,350 x 2,390 mm | 67.6 m3 | 26,840 kg |
| 40ft high cube dry (ONE) | 12,032 x 2,350 x 2,695 mm | 76.2 m3 | 28,800 kg |
| 20ft reefer (Maersk) | 5,451 x 2,290 x 2,167 mm | 27 m3 | 27,490 kg |
| 40ft high cube reefer (Maersk) | 11,580 x 2,275 x 2,415 mm | 67.5 m3 | 29,480 kg |
Two things stand out. First, a 20ft reefer holds 27 m3 against 33.1 m3 for a 20ft dry container, so refrigerated cargo gets less space than the same length of dry box. Second, carriers do not publish identical payloads. Maersk's dry container sheet lists 28,800 kg for a 40ft standard container, while ONE lists 26,840 kg. Adding payload and tare weight shows where the gap comes from: ONE's figures add up to 30,480 kg (26,840 plus 3,640) and Maersk's to 32,500 kg (28,800 plus 3,700), so the two assume different maximum gross weights. Take the figures for the container you will actually receive from your carrier, not from a general table.
Step 1: Measure the Packed Cargo
Measure the cargo as it will be loaded, with cartons, pallets and packaging, not the bare product. Record the total volume in cubic metres, the total weight in kilograms including packaging and pallets, and the length, width, height and weight of the largest single item. Count the pieces too, because a few very large pieces behave differently from many small cartons.
Step 2: List Special Needs
Write down anything that rules a container type in or out:
- a temperature range, which points to a reefer;
- a height above the door opening, which points to a high cube, open top or flat rack;
- loading from above by crane, which points to an open top;
- very heavy or oversized pieces, which may point to a flat rack or breakbulk;
- goods that must not share air or space with strong odours or moisture;
- dangerous goods, which have their own rules and must be declared.
Step 3: Compare Volume and Weight With the Container
Both numbers must fit. Compare the volume with the capacity and the weight with the payload, and leave a margin, because pallets, gaps and bracing mean you will not fill every cubic metre. If either number is close to the limit, move up a size or split the shipment. Our guide to packaging and palletizing standards shows how packing choices change the volume you need.
Step 4: Check the Door and the Internal Height
Cargo has to pass through the door, and the door is smaller than the inside. ONE lists a door opening of 2,340 mm wide by 2,280 mm high for the standard dry containers, and 2,340 mm by 2,585 mm for the high cube. Measure your tallest and widest piece with its packaging and compare it with the door, not the internal height.
Step 5: Get Quotes in More Than One Size
Ask your forwarder for prices for the sizes that could work and compare them per unit of cargo, not per container. A larger container can cost less per cubic metre but more per tonne, so the cheapest size depends on which limit your cargo reaches first. The next article in this series works through that arithmetic.
Step 6: Plan Loading, Securing and Weight
Plan how the cargo will be loaded, braced and sealed. The CTU Code, voluntary guidance from the IMO, ILO and UNECE on packing containers and other cargo transport units, is a good reference for loading and securing. Each packed container also needs a verified gross mass: the IMO says the shipper states it in the shipping document and sends it ahead of loading to both the master and the terminal. And if any packaging is raw wood, the international standard ISPM 15 requires treatment and marking.
Three Worked Examples
These examples use made-up cargo to show the method.
Example A: limited by volume. A shipment is 480 cartons, each 0.50 x 0.40 x 0.40 m (0.08 m3) and 20 kg. That is 38.4 m3 and 9,600 kg. If you assume you can use about 85% of the container's space, which is an assumption and will differ in practice, you need about 45.2 m3 of capacity. A 20ft dry container (33.1 m3) is too small. A 40ft dry container (67.6 m3) fits with room to spare, at roughly two thirds full.
Example B: limited by weight. A shipment is 22 pallets, each 0.96 m3 and 1,100 kg. That is about 21.1 m3 and 24,200 kg. The weight is within the 20ft payload of 28,330 kg and the volume is well inside 33.1 m3, so a 20ft fits. A 40ft would also carry the weight, but it would be only about 31% full by volume, so the 20ft is the better match.
Example C: limited by the door. A crated machine is 2,400 mm high, 2,000 mm wide, 3,000 mm long and 4,500 kg. Weight is no issue, but 2,400 mm is taller than the 2,280 mm door of a standard dry container and fits within the 2,585 mm door of a high cube. If the crate were taller than that, or had to be lifted in from above, an open top or flat rack would be the next options.
Mistakes to Avoid
- Choosing by volume alone and ignoring weight.
- Assuming a 40ft container carries double the weight of a 20ft.
- Forgetting the door opening and measuring only the inside.
- Using the product's size instead of the packed size.
- Filling the container on paper to 100%, with no allowance for gaps.
- Not checking road weight limits for the inland legs, which are set locally and may differ from the container's rating. Ask your forwarder or trucker to confirm them for your route.
A Short Checklist
- Measured the packed volume, weight and largest piece.
- Listed special needs such as temperature, height and loading method.
- Checked volume against capacity and weight against payload, with a margin.
- Checked the door opening.
- Asked for quotes in more than one size.
- Planned loading, securing and the verified weight.
Get Help Choosing With RR Brothers and Logistics
RR Brothers and Logistics can quote sea freight in the container size that suits your cargo and compare options side by side. Send us your cargo details with volume, weight and the dimensions of your largest piece.
Frequently Asked Questions
Measure the packed volume, weight and largest piece, list special needs such as temperature or height, compare volume with capacity and weight with payload, check the door opening, and get quotes in more than one size.
In volume it is about double: ONE lists 67.6 m3 against 33.1 m3 for standard dry containers. The payload is not double, with ONE listing 26,840 kg for the 40ft and 28,330 kg for the 20ft.
When your cargo is tall, or light and bulky. ONE lists 76.2 m3 and a door height of 2,585 mm for a 40ft high cube, against 67.6 m3 and 2,280 mm for a standard 40ft.
No. For a 40ft standard dry container, Maersk lists 28,800 kg and ONE lists 26,840 kg. Ask your carrier for the figures for the container you will actually receive.
Under SOLAS guidance from the IMO, the shipper must state it in the shipping document and submit it in advance to the master and the terminal. Ask your forwarder who supplies it and by when.
A standard container will not take it. Consider a high cube if the height fits its door, or an open top or flat rack if the cargo must be lifted in or is oversized, and talk to your forwarder early.
Sources
- ONE: Dry container specifications (20 ft, 40 ft and 40 ft high cube)
- Maersk: Dry container equipment specifications
- Maersk: Reefer container equipment specifications
- IMO: IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (CTU Code)
- IMO: Verification of the gross mass of a packed container (SOLAS)
- IPPC/FAO: ISPM 15, Regulation of wood packaging material in international trade (2018)
This article is general information, not legal, tax or customs advice. Rules, rates and procedures change; confirm current requirements with the relevant authority or a licensed customs professional before you ship. Regulatory references were checked against the official sources listed above on 25 October 2026.
Image credits: header photo by Richard Williams on Unsplash; photo by CHUTTERSNAP on Unsplash. Used under the Unsplash License.
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