Shipping Container Steel: Thickness, Gauge, and Grade Explained
| Container part | Gauge | Thickness |
|---|---|---|
| Wall panels (corrugated) | 14 gauge | 0.075 in (1.9 mm) |
| Frame, pillars, rails | 7 gauge | 0.187 in (4.75 mm) |
| Cross members (floor joists) | — | 3–4 mm (0.12–0.16 in) |
| Floor (plywood decking) | — | 28 mm (about 1-1/8 in) |
The steel itself is corten (weathering) steel, most often meeting ASTM A242 or A588.
Have you ever thought about using small shipping containers as part of your business?
Perhaps you ship products overseas, or you’ve been considering them for temporary office space or storage? Ranging from 6-10ft, small shipping containers are a low-cost alternative to more permanent structures.
It might surprise you to find out that small shipping containers come with several options: airtight metal, insulated, refrigerated, and even military-grade. You can also add a chassis to create a shipping container trailer!
How Thick Is the Metal on a Shipping Container?
The walls on small shipping containers are usually made with 14 gauge corrugated sheet steel panels. The thickness is 0.075 inches (about 1.9 mm), and these panels are welded to the rest of the structure.
The frame, pillars, and rails are 7 gauge tubular steel, which is considerably thicker at 0.187 inches (about 4.75 mm). The corner castings (or corner fittings) are reinforced openings for twist-lock connections. These enable the container to be connected to others or anchor points. They are manufactured to be strong enough for lifting by a crane rig, even when full of goods.
The cross members are the joists that support the floor on the bottom of the shipping container and are 3-4mm thick. The purpose of these beams is to lift the floor from beneath, so that moisture is unable to get into the container and it can be lifted without damage. The added benefit of this arrangement is that the shipping container can be used as an office, without the need for a foundation.
The floor itself is 28mm thick. Plywood is often screwed to the floor and is usually 1-1/8″ thick. Woven bamboo is becoming increasingly popular, due to it being less expensive.
What Gauge Steel Are Shipping Containers?
Two gauges cover almost every part of a standard container. The corrugated wall, roof, and door panels are 14 gauge steel. The structural skeleton — corner posts, top and bottom rails, and door frame — is 7 gauge tubular steel, roughly two and a half times thicker.
Remember that steel gauge runs backwards: the lower the gauge number, the thicker the metal. That is why 7 gauge framing (0.187 in) is heavier than 14 gauge panelling (0.075 in), not lighter.
The corrugation matters as much as the gauge. Pressing those ridges into the panel dramatically increases its stiffness, which is how a 1.9 mm skin can stay rigid across an 8-foot wall and carry stacking loads nine containers high.
What Steel Is Used to Make Shipping Containers?
When it comes to metal, we’re usually conditioned to think of rust as a bad thing, but the steel used in shipping containers benefits from protection when a layer of rust forms. What kind of steel is this?
Shipping containers are constructed with a type of steel known as weathering or self-healing. Also called COR-TEN (or corten), these words are sometimes used interchangeably and are a U.S. Steel trademark. The name derives from the two main properties of the steel: corrosion-resistant and tensile-strength.
As the name suggests, it’s a very strong material that is weldable and rust-resistant. When weathering steel that is painted suffers a chip or has its paint worn off by the elements, the surface rust prevents further erosion.
Corten is known as alloy steel because it contains other non-metallic elements, namely carbon, sulfur, and silicon. The metals in this type of steel are usually iron, copper, manganese, nickel, and chromium.
The motivation behind the development of corten was steel that would not need painting and would develop a rust-like exterior after years of weather exposure. With that said, corten also comes in a prepainted form, which has even more benefits, like 25-year anti-perforation.
What Grade of Steel Is Used in Shipping Containers?
“Grade” is the classification system that describes a steel’s chemistry and mechanical properties. For containers, the grade that matters is weathering steel, and it is normally supplied against one of two ASTM specifications:
- ASTM A242 — the original high-strength low-alloy (HSLA) structural steel specification, covering the shapes, plates, and bars used where added durability and corrosion resistance are needed.
- ASTM A588 — the more common modern HSLA weathering specification, covering structural steel with a 50 ksi minimum yield strength in the thicknesses used for container framing.
Both rely on the same trick: small additions of copper, chromium, and nickel let the surface form a tight, adherent oxide layer that seals itself instead of flaking away like ordinary mill scale.
One standard people often mistake for a steel grade is ISO 6346. That is the international rule for how a container is coded, identified, and marked — the owner prefix and check digit on the door — not a description of the metal itself.
The practical takeaway for a buyer: corten construction is what gives a container a 25-year-plus service life outdoors with no foundation and no annual painting. It is also why surface rust on a used unit is usually cosmetic rather than structural — though you should still inspect the frame, door seals, and floor before you buy.
Shipping Container Materials Compared: Steel vs Aluminum vs Composite
Steel is the default, but it is not the only material containers are built from. Here is how the three compare.
Steel. Exceptional strength and stacking capacity, decades of service life, universally repairable by any welder, and the cheapest of the three to buy. The trade-offs are weight, which raises delivery cost, and susceptibility to corrosion at scratches and welds in coastal or humid sites.
Aluminum. A far better strength-to-weight ratio and inherent corrosion resistance, which makes it attractive where transport weight or salt air dominates. It is weaker in absolute terms, less tolerant of heavy point loads, more expensive per unit, and harder to find and repair. If you are weighing this specific trade-off, see our detailed comparison of steel and aluminum shipping containers.
Composite. Fiber-reinforced composites are the newest option: light, corrosion-proof, and often made with recycled or renewable content. They remain a niche product — production cost is high and availability is limited, so sourcing and later resale are both harder than for a standard steel box.
For the overwhelming majority of storage and site-office uses, steel remains the right answer on cost, availability, and repairability. Prices move with the scrap and freight markets, so check a current delivered-price estimate rather than relying on a published figure.
Are Shipping Containers Bulletproof?
While a standard shipping container isn’t designed to be bulletproof, the National Geographic show ‘Doomsday Preppers’ tested it out. They found that it would indeed stop a .22 caliber long rifle round.
The Canadian YouTube channel ‘Civil Advantage’ tested out even more bullets and found out that a shipping container could also stop a 9mm hollowpoint and 12 gauge buckshot. Here are the bullets that it couldn’t stop:
- PolyCase
- 9mm FMJ
- 5.56 Frangible
- .223 JHP
- 12 gauge slug
How Long Can a Steel Shipping Container Last?
Because the weather conditions at sea are so harsh, most shipping companies will sell their shipping containers after 10-20 years. After that, they are often purchased for alternative use and can provide many more years of service. When used as a storage unit, a shipping container will be exposed to less extreme weather throughout its lifespan.
The common average for lease/rental containers might be 10-12 years, but a storage container can last 25-30 years, with some reporting as many as 50 years.
Several factors will affect the durability of small shipping containers. The most important factors are how well you treat it and if the exterior is well-painted or maintained, perhaps by using insulation measures like cladding.
Will a Shipping Container Protect Against EMP?
An electromagnetic pulse (EMP) is a short burst of energy and can be either natural or man-made. Depending on the source, it could be radiation, an electric/magnetic field, or a conducted electrical current.
Interference from an EMP can disrupt or damage electronic gear and powerful events like a lightning strike can damage buildings. How do small shipping containers hold up to an EMP?
Because it’s exterior is entirely metal, a shipping container has excellent potential as a faraday cage. For the same reason, you’re relatively safe in your car during a lightning storm. The caveat is, that you mustn’t touch anything metal that will conduct the EMP to your body.
As long as the metal base of the shipping container is in contact with the earth, then the container is electrically grounded.
To be fully shielded from the effects of an EMP, you would need to make sure that you or your electronics don’t touch the metal walls. If you don’t have a wooden floor, you would need a thick carpet or rugs to shield you and your gadgets.
Need Small Shipping Containers?
We’ve shown that small shipping containers are versatile in use and durable in the elements. Don’t store valuable items in a more expensive, but less-secure wooden shed. Shipping containers have an excellent ability to stay dry, they are not a fire risk, and they’re better equipped to keep rodents and insects out.
If you require small shipping containers for commercial or residential use, we can help you out. We are a nationwide solution for renting and buying steel storage containers, Conex boxes, and metal shipping containers.
Get a quote and compare prices.
My brother and I want to get a shipping container and modify it into a shed. We need to attach it to other metal parts we have found. Thanks for making it clear that they are weldable and rust-resistant so we know how to go about modifying it.