The Container
Reference.
Everything technical about steel shipping containers (also known as conex boxes or sea cans) in plain English: real dimensions, how to read the markings, and what a used Wind & Water Tight box actually is.
Container Dimensions & Specifications
Standard sizes per ISO 668:2020, except the 10ft row, which is the common 8'6" trade build rather than an ISO 668 size. We sell the three marked “We sell” as Wind & Water Tight (used); the rest are here for reference.
| Size | External (L×W×H) | Interior L | Interior W | Interior H | Door (W×H) | Capacity | SBD |
|---|---|---|---|---|---|---|---|
| 10ft (common trade build, not ISO 668) | 9'9.75" × 8'0" × 8'6" | 9'3" | 7'8.5" | 7'10.1" | 7'8.1" × 7'5.8" | 561 cu ft | Reference |
| 20ft Standard | 19'10.5" × 8'0" × 8'6" | 19'4.2" | 7'8.5" | 7'10.1" | 7'8.1" × 7'5.8" | 1,172 cu ft | ✓ We sell → |
| 20ft High Cube | 19'10.5" × 8'0" × 9'6" | 19'4.2" | 7'8.5" | 8'10.1" | 7'8.1" × 8'5.8" | 1,320 cu ft | Reference |
| 40ft Standard | 40'0" × 8'0" × 8'6" | 39'5.7" | 7'8.5" | 7'10.1" | 7'8.1" × 7'5.8" | 2,387 cu ft | ✓ We sell → |
| 40ft High Cube | 40'0" × 8'0" × 9'6" | 39'5.7" | 7'8.5" | 8'10.1" | 7'8.1" × 8'5.8" | 2,691 cu ft | ✓ We sell → |
| 45ft High Cube | 45'0" × 8'0" × 9'6" | 44'5.7" | 7'8.5" | 8'10.1" | 7'8.1" × 8'5.8" | 3,037 cu ft | Reference |
- 10ft (common trade build, not ISO 668): Far fewer 10ft containers are in circulation than 20ft or 40ft, so used ones are hard to find. A 10ft is a special request for us: ask and we will tell you what we can find.
- 20ft High Cube: Uncommon in the used market; usually one-trip/new.
- 40ft High Cube: In 40ft, the High Cube is more common than the standard height.
- 45ft High Cube: High-cube only; usually needs an oversize permit or extendable trailer to move.
Comparing footprints? See the complete 10ft-45ft size chart.
How to Read a Container’s Markings
Every container is stamped with a standardized identity under ISO 6346. Here’s what the letters and numbers mean.
The 11-character ID number
| Part | What it means |
|---|---|
| Owner Code (3 letters) | The registered owner/operator prefix, issued through BIC (bic-code.org). |
| Equipment Category (1 letter) | U = freight container · J = detachable freight-container equipment · Z = trailer or chassis. |
| Serial Number (6 digits) | The individual unit's number, assigned by the owner. |
| Check Digit (1 boxed digit) | A math-derived digit (shown in a box) that validates the other 10 characters. |
Have a container number? Check it in seconds with our free check digit calculator.
Check a container number →To see who owns a prefix, search the BIC register. Our guide to free BIC lookups for a used container walks through it.
The 4-character size & type code
1st char: length
- 1 10ft
- 2 20ft
- 3 30ft
- 4 40ft
- L 45ft (newer BIC tables list 45ft as 5; most 45ft boxes in service are still marked L, e.g. L5G1)
2nd char: height / width
- 0 8'0" high
- 2 8'6" high (standard)
- 4 9'0" high
- 5 9'6" high (high cube)
- 8 4'3" high (half-height)
- 9 4'0" high or less
- C 8'6" high & over 8' wide
3rd-4th chars: type
- G0 / G1 General-purpose dry van (G1 = passive-vented)
- V0 / V2 Mechanically ventilated
- U0 / U1 Open-top
- P1 / P3 Flat rack / platform
A worked example: CSQU 305438 3, 45G1
Here is one full set of markings, read part by part. The ID is a widely used example number. We paired it with a 45G1 code to show both parts together.
CSQU 305438 3
45G1
| Characters | Part | What it means |
|---|---|---|
CSQ | Owner code | The 3-letter prefix registered with BIC. |
U | Category | U means a freight container. |
305438 | Serial number | This unit's number in the owner's fleet. |
3 | Check digit | Worked out from the 10 characters before it. It is shown in a box. |
4 | Length | 40ft long. |
5 | Height | 9'6" high, which is a high cube. |
G1 | Type | General purpose, with passive vents. |
Want to see the check digit math? Run this number through the check digit calculator for the full arithmetic.
Common full size and type codes
You will see these full codes most often. Each one reads left to right, using the parts above.
| Code | What it means |
|---|---|
22G1 | 20ft standard, 8'6" high, general purpose with vents |
42G1 | 40ft standard, 8'6" high, general purpose with vents |
45G1 | 40ft high cube, 9'6" high, general purpose with vents |
L5G1 | 45ft high cube, 9'6" high, general purpose with vents |
22U1 | 20ft open top |
22P1 | 20ft flat rack with fixed ends |
22R1 | 20ft refrigerated container (reefer) |
These codes come from ISO 6346. The BIC publishes the code parts on its size and type code page.
Weight and capacity markings
Most containers also show weight and volume markings on the doors.
| Marking | What it means |
|---|---|
MAX GROSS | The most the container and its cargo may weigh together. |
TARE | The weight of the empty container. |
PAYLOAD (or NET) | The cargo weight marked for that unit when it ships. It equals max gross minus tare. |
CU. CAP. | The inside volume, usually shown in cubic meters and cubic feet. |
For a buyer, tare is usually the number to know. It is what the empty box weighs on the delivery truck. Payload is the cargo limit marked for shipping.
The CSC Safety Approval Plate
Required under the IMO International Convention for Safe Containers, the CSC plate is the container’s “passport”: it records structural approval and inspection history and stays with the unit into the used market.
The plate records:
- The country of approval and the approval reference
- The date of manufacture
- The manufacturer's identification number for the container
- The maximum operating gross mass
- The allowable stacking load
- The transverse racking test load
- An examination date, or an ACEP number if the container is on an approved continuous examination program
The plate is about international shipping. Our used Wind & Water Tight containers are sold for storage and are not certified for ocean shipping. For more on the plate and who needs one, see our container certification guide.
Want to decode the rest of the stampings? Here’s how to read the full ID number and run the check digit yourself.
Lifecycle: Why a Used Box Is a Smart Buy
A Wind & Water Tight container is retired from the sea, not worn out. Here’s why used steel holds up.
Built from weathering steel
Shipping containers are made from Cor-Ten (weathering) steel, which forms a stable, non-porous patina as it ages. That's why the surface rust you see on a used box is usually cosmetic, not structural: the steel is protecting itself.
Decades of service life
A container spends years in active maritime service, then can serve for decades in static land use with basic maintenance. A Wind & Water Tight unit is retired from the sea, not worn out.
Why used units are abundant
North America imports far more containerized freight than it exports, and repositioning empty boxes back overseas costs more than building new ones. So shipping lines sell them off here, which is why a good used container is widely available and a smart-value buy.
See exactly what we sell → our condition guide.
Reference FAQ
What do the numbers on a shipping container mean?
Every container carries an 11-character ID under ISO 6346: a 3-letter owner code registered with BIC, a 1-letter equipment category (U for freight containers), a 6-digit serial number, and a boxed check digit that validates the rest.
How do I read a container's size and type code?
The 4-character size/type code sits below the ID. The first character is length (2 = 20ft, 4 = 40ft, L = 45ft; newer BIC tables list 45ft as 5, but most 45ft boxes in service are still marked L, e.g. L5G1), the second is height/width (2 = 8'6" standard, 5 = 9'6" high cube), and the last two describe the type (G1 = general-purpose dry van).
What is the CSC plate on a shipping container?
The CSC Safety Approval Plate, required under the IMO International Convention for Safe Containers, is the container's passport: it records structural approval and inspection history and stays with the unit into the used market.
Is surface rust on a used container a problem?
Usually not. Containers are built from Cor-Ten weathering steel that forms a protective patina, so surface rust is typically cosmetic. Every container we stock is Wind & Water Tight: it keeps out rain, wind, snow, and pests, with no holes and doors that seal.
Can the check digit catch a wrong container number?
Usually, yes. Each of the first 10 characters becomes a number and is weighted by its position. The total is divided by 11, and the remainder is the check digit, with a remainder of 10 written as 0. Most typos change the result, so the number stops matching.
What does 45G1 mean on a shipping container?
It is the size and type code. The 4 means 40ft long. The 5 means 9'6" high, which is a high cube. G1 means general purpose with passive vents. So 45G1 is a standard 40ft high cube.
What is the difference between max gross, tare, and payload?
Max gross is the most the container and its cargo may weigh together. Tare is the weight of the empty container. Payload is max gross minus tare: the cargo weight marked for that unit when it ships.
What if a used container has no CSC plate?
For storage, it does not matter. The CSC plate is required for containers in international transport. It is not needed for storage or for a truck delivery that stays within the United States. If you plan to ship a box overseas, ask about the plate before you buy.
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