Anyone who's shopped for a shipping container or works around them is aware of the conventional 20' and 40' containers sizes, but what many people don't know is how and why other container sizes are used and occasionally available in the market. Non-international sizes like 10', 48', and 53' shipping containers are common in some markets, although their size limits their international mobility and usage.
In the 1960's the International Standards Organization, or ISO, mandated the standards for container dimensions. Originally they were set to 10', 20', 30', and 40' long, 8' wide, and 8' 6" tall. As many people are aware, the 10' and 30' never caught on and have never really been used in international shipping (except for the recent growth in popularity of the 10' containers, but that's a unique case). High cube containers have grown in popularity recently as they allow an additional foot in height (9' 6”).
In order to be more competitive with the American trucking industry, in 1985 APL introduced the 48' and 53' containers. This helped to offset the difference as the trucking industry moved to 48' and 53' containers. These containers aren't only longer, but they were also wider at 8' 6”; and while they were able to help keep a competitive edge, this size of container was too large for other markets and is now referred to as American domestic containers and never became a global standard. To adopt any chance in container size there would be a great amount of infrastructure that would have to be retooled: trains, trucks, chassis, vessels, and almost any equipment relating to the industry.
America isn't the only market that's created a domestic container size; Europe and Australia have also tweaked their sizes slightly to better accommodate their domestic needs. In Europe, shipping containers maintain the standard ISO length, albeit measured in meters; however they are slightly wider at 2.5m and 2.55m to allow two pallet widths to be stacked inside side by side. Australia has closer standards to the United States' 48' and 53' units.
As the popularity of repurposed shipping containers grew, either for portable storage, housing, or other projects, so did the demand for 10' shipping containers. However, 10' containers are a unique case. Almost every container shipping line is geared to handle 20' containers and 40' containers, which would make 10' containers a problem. They way that container manufacturers have navigated around this problem is to weld two 10' containers together at the factory, thus making one 20' container. This pushes the burden of loading the container onto the logistics company or shipping line. Once the 2x 10' containers arrive at the depot they're separated at the welded joints and can be sold separately.
The international standardization of container sizes allows goods and products to be freely transported around the world, at the most cost efficient manner. Without standardization each shipping line could use containers of different sizes and specifications, which in the end would drive up the price of the goods inside of the containers. Keep that in mind the next time you see a 40' or 53' container on the highway or loading doc. All of the specifications are printed on the back door and you can see for yourself if it's a domestic or international container.