A standard 20ft container runs about 20 feet long, 8 feet wide and 8.5 feet tall outside, and empty it weighs somewhere around 2,300 kg, though it moves a bit depending on who built it and when. A 40ft is double the length and weighs roughly 3,750 kg empty. And the part that surprises almost everyone the first time they hear it is that the bigger box does not carry more weight than the small one, it only carries more space, because both sizes share the same gross weight rating. That one fact decides more container bookings than anything else in this guide, so keep it in mind while reading the rest.
The Sizes You Will Actually Deal With
On paper there are a lot of container sizes, 10ft boxes for storage yards, 45ft high cubes on certain lanes, 53ft units that live mostly on North American rail. In real bookings you will see three, and it is the same three everywhere. The 20ft standard, the 40ft standard, and the 40ft high cube, which is the identical footprint to a 40ft with an extra foot of height, 9.5 feet outside instead of 8.5. That extra foot buys you another eight or nine cubic metres inside for barely any extra steel, and if your cargo is light and bulky, furniture, garments, packaging, that space costs you almost nothing and earns its keep on every trip.
Width never changes though. Every ISO box is 8 feet wide outside and about 2.35 metres inside, and it stays fixed because every ship cell, crane spreader, chassis and rail wagon on the planet was built around that number.
Tare, Payload And Max Gross
Three weights, and people mix them up constantly.
- Tare weight is the empty container itself, steel, floor, doors and all.
- Payload is the cargo weight the box is designed to hold.
- Max gross is the two added together, the heaviest the loaded box is allowed to be.
You never have to guess them either, because every ISO container carries a CSC plate riveted to the door with the tare and max gross stamped on it. One warning from people who buy used boxes, if a container has been modified, insulated, panelled, wired up, the plate still shows the original factory tare, so the real empty weight can sit above what is stamped and nobody updates the plate for you.
The typical figures, which vary a little by manufacturer and age:
| Container | External Size (L x W x H) | Tare Weight | Max Payload | Max Gross |
|---|---|---|---|---|
| 20ft Standard | 6.06 x 2.44 x 2.59 m | 2,200 to 2,360 kg | up to ~28,000 kg | 30,480 kg |
| 40ft Standard | 12.19 x 2.44 x 2.59 m | ~3,750 kg | ~26,700 kg | 30,480 kg |
| 40ft High Cube | 12.19 x 2.44 x 2.90 m | 3,900 to 4,300 kg | ~26,500 kg | 30,480 kg |
| 10ft Storage | 2.99 x 2.44 x 2.59 m | ~1,200 kg | ~9,000 kg | ~10,160 kg |
Inside dimensions run a few inches smaller on every axis, so a 20ft gives you around 33 cubic metres of usable space and a 40ft about 67. And check the door opening before you book anything bulky, because the doorway is narrower and shorter than the interior, roughly 2.34 m wide and 2.28 m high on a standard box, and machinery has absolutely failed to fit through a door that its crate technically had room for once inside.
Why The Small Box Carries As Much As The Big One
Look at the table again. All three main sizes share the same 30,480 kg max gross, because the ISO standard rates the frame and corner castings the same across both lengths, and since the 40ft weighs more empty, its payload ceiling actually comes out lower than the 20ft. Some carriers even rate their 20 footers all the way up to 28 tonnes of payload, Maersk publishes 28.2 on its own spec sheet.
So dense heavy cargo, steel coils, machinery, tiles, minerals, goes in 20ft boxes, because you hit the weight limit long before the walls, and light bulky cargo goes in 40ft or high cube boxes because you fill the space long before the scale complains. Shippers call the first situation weighing out and the second cubing out, and once you know which one your cargo does, the size choice mostly makes itself.
The Number On The Box Is Not What The Road Allows
Now the part that catches even experienced importers when they land in a new market. That max gross stamped on the container is a structural rating, it tells you what the box survives at sea stacked under other loaded boxes. It says nothing about what a truck can legally haul on a road, and road law is nearly always the lower ceiling.
Take the United States, where truck, chassis and loaded container together have to stay under the 80,000 lb federal limit, and once the tractor and chassis eat their share, the cargo you can practically load usually lands well under what the container is rated for, commonly quoted somewhere in the high 30s of thousands of pounds for a 20ft and low 40s for a 40ft, though it shifts with the equipment, the axles and the state, so treat those as ballpark and confirm with your trucker rather than with me. Other countries run their own axle and gross vehicle rules and they differ enough that a load rolling legally out of one port can be overweight at the destination. If your cargo is heavy, ask about road limits at both ends before loading, because fixing it after means unpacking a sealed box in a port somewhere.
And on the subject of weight and rules, since 2016 no container gets loaded on a ship without a Verified Gross Mass declared to the carrier, the SOLAS rules brought that in after years of misdeclared weights causing stack collapses. You either weigh the packed box on a certified scale or weigh the cargo plus packaging and add the plate tare, and the figure travels with the booking. Terminals hold or refuse boxes with missing or obviously wrong VGM, so it is not paperwork you can shrug at.
Which Size To Book
My take. If the cargo is dense, book the 20ft and stop thinking about it, the payload ceiling is the same or better and the box is cheaper to move, position and store. If the cargo is light and you are anywhere near 25 cubic metres, go straight to the 40ft high cube rather than the standard 40ft, since on a lot of lanes the price gap between the two is small and the extra height is the cheapest space you will find anywhere in shipping. That leaves the standard 40ft as the box I would only book when a route or a stack of them on a multi container move specifically calls for it, and you are free to disagree once you have priced your own lane.
Measure the cargo, weigh it properly, confirm the road rules at both ends. The container itself is the one part of this that has not changed in decades.
