Shipping container sizes and how much really fits

Container dimensions come in two flavors: the outside measurements, which are standardized by ISO 668 and identical worldwide, and the inside measurements, which vary slightly by manufacturer and age. Loading uses the inside figures, and the gap between the two is bigger than most people expect.

A 20 ft container is 6.06 meters long on the outside and about 5.89 meters inside. That 17 centimeters is the wall thickness, and it is the difference between a cargo plan that works and one that does not.

Internal dimensions and capacity

Dimensions verified Sep 24, 2026. Individual containers vary by a few centimeters; check the specific box where the fit is tight.

Why practical capacity is so much lower

The geometric cube of a 20 ft container is about 33 cubic meters. Forwarders quote 25 to 28. That is not conservatism, it is what actually loads.

Three things eat the difference. Cartons rarely tile a rectangular space perfectly, so there is waste in every direction. Cargo needs bracing, dunnage and airbags to survive the voyage, and those occupy space. And the door opening is smaller than the interior, so the last portion of the box is awkward to fill.

The 40 ft high cube is the outlier worth knowing. It has the same floor as a 40 ft standard but 30 centimeters more height, which for many carton sizes buys an extra layer and around 15 percent more capacity for a small premium.

Choosing between LCL and a full container

Below about 13 cubic meters, LCL is normally cheaper: you pay for the space you use and share the box. Above it, a 20 ft container often costs about the same as the equivalent LCL volume while moving faster, because it skips consolidation at origin and deconsolidation at destination.

The crossover is not a fixed number. It moves with the trade lane, the season and how full the carrier is. When you are near the line, get both quotes. The CBM calculator will tell you which container your volume fits and what share of it you would use.

Weight limits matter as much as space

Dense cargo hits the payload limit long before it fills the space. A 20 ft container typically has a maximum payload around 28 tonnes, and road weight limits at either end are often stricter than the container rating.

In practice, if your cargo is heavier than about 850 kilograms per cubic meter, weight will decide your container count rather than volume. Tiles, stone, machinery, liquids and printed paper all fall in that territory.

Door openings are smaller than the interior

The figure that catches people out is not the length, it is the door. A 20 ft container is about 235 cm wide and 239 cm tall inside, but its door opening is roughly 234 cm wide and 228 cm high. A 40 ft high cube has 269 cm of interior height and a door about 258 cm high.

That gap of 10 to 11 centimeters decides whether a tall machine goes in at all. Anything that has to be driven or rolled in has to clear the door, not the ceiling, and once inside it cannot be lifted into the extra headroom. If your cargo is close to the limit, measure the door and add a few centimeters for the floor of whatever is carrying it.

Payload limits by container

Every container has a maximum gross weight set by its rating plate, and the payload is that figure minus the container’s own tare weight.

Notice that a 40 ft holds twice the volume of a 20 ft but barely more weight. That is the single most useful fact in this table. Heavy, dense cargo fills a 20 ft on weight while the box still looks half empty, and shipping it in a 40 ft buys you nothing but a larger bill.

Road limits at either end are often stricter than the container rating. Many US states cap a loaded container on a chassis well below 28 tonnes once the tractor and chassis are counted, so a container that is legal at sea can be undeliverable by road. Confirm the inland limit before you load to the plate.

Volume or weight: which one decides

Divide your total weight in kilograms by your total volume in cubic meters. That number tells you which constraint you will hit first.

Under ~500 kg/m3   volume runs out first  (the usual case)
500 - 850 kg/m3    the two roughly balance
Over ~850 kg/m3    weight runs out first

Furniture, packaging, textiles and empty containers sit in the first band and fill the space long before the plate. Tiles, stone, machinery, liquids, printed paper and canned goods sit in the third, and those containers ship visibly part full. If you are in the middle band, get the loading plan right, because small changes in packing will flip which limit binds.

Containers beyond the standard three

Most ocean freight moves in the three boxes above, but a few specials are worth knowing about because they change the arithmetic entirely.

• 45 ft high cube. About 1,358 cm long inside, so roughly 13% more floor than a 40 ft at a similar payload. Not available on every lane, and some inland road networks will not take it.
• Reefer. The refrigeration unit eats roughly a meter of length and some height, so a 40 ft reefer loads closer to a short 40 ft than a standard one. Never plan a reefer from standard dimensions.
• Open top and flat rack. For cargo that cannot go through the door. You gain access but lose stackability, and both usually price well above a standard box.

Practical loading advice

• Plan to the inside dimensions. Use the table above, not the nominal 20 or 40 feet.
• Try every orientation. The container load calculator tests all six, and the gap between best and worst is often 20 percent.
• Account for pallets separately. If cargo ships palletized, you are fitting pallets, not cartons, and the deck height costs you a layer.
• Leave door clearance. The door opening is shorter than the interior height; the last section cannot be packed to the ceiling.
• Distribute weight evenly. An unevenly loaded container can be legal at sea and illegal on the road at destination.

Rules last checked: Sep 24, 2026

Estimate only. Confirm with your carrier before booking.