Conex Box vs Shipping Container: Is There a Difference?

Search for containers in the US and you see several names for the same steel box. One seller calls it a conex box, the next a shipping container, a third a sea can or a storage container. In most listings they mean exactly the same thing.

There are a few differences worth knowing, though: between the original Army CONEX and today’s containers, and above all between a real ISO shipping container and a box built only for storage. This guide explains both.

Key takeaways

• Today, conex box and shipping container usually mean the same thing: a standard steel ISO container.
• The name comes from the US Army’s CONEX, short for Container Express, introduced in 1952 and much smaller than today’s containers.
• Modern containers follow ISO standards: 8 feet wide, mostly 20ft or 40ft long, with corner castings for lifting and locking.
• The real difference to watch for is between an ISO shipping container and a box built only for storage.
• A CSC plate and an ISO container number show that a container was built and tested to the international standard.

Where the word conex comes from

CONEX stands for Container Express. The US Army developed the system after a steel box called the Transporter proved itself during the Korean War, and introduced it in late 1952. A CONEX was much smaller than a modern container: about 8ft 6in long, 6ft 3in wide and 6ft 10½in high, with a capacity of about 9,000 pounds. The Army had about 100,000 of them in service by 1965 and more than 200,000 two years later, many of them in Vietnam.

The name outlived the original boxes. Across the US, conex box is still used for any steel shipping or storage container, while the rest of the world mostly says shipping container.

The original CONEX vs a modern ISO container

International standards for containers were published between 1968 and 1970. Since then, containers have the same width, the same corner castings and the same markings everywhere, so cranes, ships, trains and trucks can handle them the same way in any port.

Conex box, shipping container, sea can: what the names mean

The real difference: ISO container or storage-only box

Some boxes sold as conex boxes or storage containers were never built for shipping. They are made for storage only, often from thinner steel, and carry no CSC plate, the safety approval that certifies a container for international transport. Such a box can work as a simple garden shed, but it is not suitable for stacking, heavy modifications or transport with cargo inside, and it is worth less when you sell it.

Before you buy, check these points:

• A CSC safety plate on the door, with the manufacturer, the date of manufacture and the weights
• A container number of four letters ending in U, followed by seven digits, on the doors and the roof
• Corner castings at all eight corners
• Corrugated steel walls and a marine plywood floor
• The grade in writing: new one-trip, cargo worthy or wind and watertight

Which should you buy?

For storage, a modification or a home, buy a new or used ISO shipping container. You get standard dimensions, real strength and a resale value, whatever the seller calls it. Our guide to the conex box explains sizes and uses, and our guide to used shipping containers explains the grades. Most buyers choose between a 20ft shipping container and a 40ft shipping container.

Listings

ISO containers available now

Standard ISO shipping containers in the grades buyers ask for most, with current starting prices at US depots. Vetted local suppliers quote delivery to your ZIP code.

Depot prices updated October 2026

Used

20ft Used Container

Cargo worthy (CW)

Structurally sound, wind and watertight and fit for shipping. A safe all round choice for storage and job sites.

20′ x 8′ x 8’6″ · 1,170 cu ft

from $1,045

Most metros $1,295 to $1,645 · depot price

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New

20ft New Container

One-trip

Shipped once from the factory. As-new condition for homes, offices and branded projects.

20′ x 8′ x 8’6″ · 1,170 cu ft

from $2,245

Most metros $2,495 to $2,595 · depot price

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Used

40ft Used Container

Cargo worthy (CW)

Twice the floor space of a 20ft at a lower price per square foot. Great for business stock and farm storage.

40′ x 8′ x 8’6″ · 2,390 cu ft

from $1,395

Most metros $1,595 to $1,945 · depot price

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Used

40ft High Cube Used

Cargo worthy (CW)

Extra foot of height for racking and bulky goods, at used container prices.

40′ x 8′ x 9’6″ · 2,690 cu ft

from $1,495

Most metros $1,745 to $2,045 · depot price

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Starting prices at the depot, based on current inventory at major US container depots. Delivery, sales tax and local fees are extra and depend on your ZIP code. Your supplier confirms the final price in your quote.

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Frequently asked questions

Is a conex box the same as a shipping container?

In almost every US listing, yes. Conex box is an American name for a steel shipping container. Check the CSC plate and the container number to be sure you get a real ISO container and not a storage-only box.

Why are shipping containers called conex boxes?

The name comes from the US Army’s CONEX, short for Container Express, a smaller steel box introduced in 1952. The word stuck and is still used for any steel container in the US.

What size is a conex box?

Today, the same as a shipping container: mostly 20ft or 40ft long and 8ft wide, in standard or high cube height. Smaller 8ft and 10ft units are also sold as conex boxes.

Are conex boxes waterproof?

A container graded wind and watertight or cargo worthy keeps out rain and wind. Check the door seals and the roof before you buy, especially on older used units.

Can I still buy an original Army CONEX?

Original CONEX boxes are rare today and mostly bought by collectors. For storage or a project, a standard ISO container is the practical choice.

shipping-containers.com is a marketplace, not a dealer or a builder. Send one request with your ZIP code and the containers you need, and vetted local suppliers respond with delivered prices. One request, multiple quotes, no fees. Compare sizes and grades on shipping containers for sale.