Container sizes are standardised in ISO 668, which is why a box from Shanghai fits a truck chassis in Rotterdam. But the brochure figures hide two traps. The door opening is lower than the internal height, so the door decides how tall your pallets can be. And the cubic capacity (CBM) is a geometric maximum you never reach with real cargo. This page gives the numbers for every common type, then the practical loading rules. If you're booking ocean freight, this is the homework before you pick a box.
The four standard dry boxes
Figures below are nominal values from the Hapag-Lloyd container specification; expect a few centimetres of variation between series and manufacturers. All metric, L × W × H.
| 20' standard | 40' standard | 40' high cube | 45' high cube | |
|---|---|---|---|---|
| External | 6.06 × 2.44 × 2.59 m | 12.19 × 2.44 × 2.59 m | 12.19 × 2.44 × 2.90 m | 13.72 × 2.44 × 2.90 m |
| Internal | 5.90 × 2.35 × 2.39 m | 12.03 × 2.35 × 2.39 m | 12.03 × 2.35 × 2.70 m | 13.56 × 2.35 × 2.70 m |
| Door opening (W × H) | 2.34 × 2.28 m | 2.34 × 2.28 m | 2.34 × 2.58 m | 2.34 × 2.58 m |
| Capacity | 33.2 m³ | 67.7 m³ | 76.3 m³ | 86.0 m³ |
| Max payload | ± 28,200–30,200 kg | ± 26,700–28,800 kg | ± 28,600 kg | ± 27,800 kg |
A 20' high cube exists too (2.90 m external, around 2.70 m internal height), but it's a niche unit most carriers barely stock. If you need height on a 20' booking, ask early or split over a 40' HC.
Note the payload pattern: a 20' often carries more weight than a 40'. Volume scales with length, weight allowance doesn't. Heavy, dense cargo goes in a 20'; light, voluminous cargo wants a 40' HC.
The door is lower than the ceiling
The single most common loading mistake: planning pallet height against the internal height. You don't lower cargo in from above, you drive it in through the door, and the door header sits roughly 10 cm below the ceiling.
- Standard (20'/40'): internal height 2.39 m, but the door is about 2.28 m. Plan loaded pallets at 2.20 m or less, so the forklift has room to lift, tilt and clear the door sill.
- High cube (40'/45' HC): internal 2.70 m, door about 2.58 m (Hapag-Lloyd lists 2,597 mm). Plan loaded pallets at 2.50 m or less.
The geometric maximum is the door height minus a few centimetres; the workable maximum is lower because a forklift carries the pallet slightly raised and tilted back. A 2.35 m pallet that "fits" the internal height of a standard box will not go through the door. That cargo needs a high cube, full stop.
Pallets on the floor: euro and block
Two pallet footprints dominate: the euro pallet (1.20 × 0.80 m) and the block or industrial pallet (1.20 × 1.00 m). The internal width of 2.35 m is the constraint: two pallets lengthwise next to one crosswise is how the classic euro-pallet pattern works out.
| Single layer on the floor | 20' | 40' / 40' HC |
|---|---|---|
| Euro pallets (1.20 × 0.80 m) | 11 | 24–25 |
| Block pallets (1.20 × 1.00 m) | 9–10 | 20–21 |
The 11 in a 20' comes from one row of 7 turned crosswise plus one row of 4 lengthwise. In a 40' the same pattern gives 25 on paper; 24 is the comfortable count when you want working clearance at the door. A high cube adds nothing on the floor, only height, which matters once you can double-stack low pallets.
For the road leg before or after the sea voyage, the same footprint maths converts into loading metres on a trailer.
Weight beats floor space
Before you celebrate fitting 25 pallets: 25 pallets at 1,200 kg each is 30 tonnes, which is over the payload of most 40' units. With dense cargo the weight limit bites long before the floor is full, and on top of the box limit come road weight limits in the countries the container crosses. The declared, verified weight (VGM) has to match what's actually inside, so do this sum at booking, not at the terminal.
CBM: brochure figure versus what you really load
The capacity column above is pure internal volume. Real-world stuffing never reaches it:
- Loose-loaded cartons, well stacked: around 85% is achievable. Call it 27–28 m³ in a 20', 55–58 m³ in a 40'.
- Palletised cargo: usually 65–75% of the volume, because pallets eat height and leave gaps. A 40' HC with 24 euro pallets at 2.20 m load height carries about 50 m³ of actual product.
When you compare quotes per CBM or decide between one 40' and two 20's, calculate with the realistic figure for your packing style, not the brochure number.
Reefers: smaller inside than they look
A refrigerated container carries its cooling unit and insulation inside the same external frame, so you lose volume in every direction. There's also a red load line: stow above it and the air circulation fails, and so does your cargo.
| 20' reefer | 40' HC reefer | |
|---|---|---|
| Internal (L × W × H) | ± 5.45 × 2.29 × 2.27 m | ± 11.58 × 2.29 × 2.54 m |
| Max stow height (load line) | ± 2.18 m | ± 2.42 m |
| Door opening (W × H) | ± 2.29 × 2.26 m | ± 2.29 × 2.56 m |
| Capacity | ± 28 m³ | ± 67 m³ |
| Max payload | ± 27,500–29,100 kg | ± 29,500 kg |
So a "40 ft" reefer is internally closer to 11.6 m than 12 m, and euro-pallet counts drop accordingly (typically 9–10 in a 20', 23 in a 40' HC reefer). Check the carrier's sheet for the exact unit.
Specials: open top, flat rack, platform, tank
| Type | What it's for | Key figures |
|---|---|---|
| Open top 20'/40' | Over-height cargo, crane loading from above | Internal footprint as a dry box; ± 2.38 m height under a removable tarpaulin; payload ± 30 t (20') / ± 28.5 t (40') |
| Flat rack 20' | Heavy, out-of-gauge machinery | Floor ± 5.6 × 2.2 m between corner posts; payload up to ± 42 t |
| Flat rack 40' HC | Long and heavy out-of-gauge pieces | Floor ± 11.65 × 2.2 m; payload up to ± 54 t |
| Platform | Over-width or extreme weight, no walls at all | 20': 6.06 × 2.44 m; 40': ± 12.19 m long; payloads as the flat racks |
| ISO tank 20' | Bulk liquids (chemicals, foodstuffs) | 20' frame, typically 21,000–26,000 litres; must be filled to at least 80% (surge) and never 100% (expansion) |
Anything that doesn't fit inside a closed box changes the booking: out-of-gauge cargo takes extra slots on the vessel and is priced accordingly, so flag dimensions to your forwarder before fixing the deal, whatever the Incoterm.
Matching the box to the cargo
Nexport Logistics, freight forwarder under the FENEX conditions, runs this check on every booking in Nexportal: pallet heights against the door, weight against payload and road limits, CBM against the realistic fill rate. The result is the cheapest container that actually fits, instead of a surprise at the warehouse door.
Got cargo and not sure if it's a 40' HC or a flat rack case? Send the dimensions to info@nexportlogistics.nl and you'll get a straight answer.
Sources: Hapag-Lloyd Container Specification (PDF) · DSV — Dry container dimensions · ColliCare — How many pallets fit in a container · ISO 668. Related: Sea Freight · Vgm · Loading Metres