What Is a Conex Box?
A Conex box is a corrugated steel shipping container manufactured to International Organization for Standardization (ISO) specifications so it can stack and lock uniformly on ships, rail cars, and chassis trailers. The term “CONEX” is short for “Container Express,” a designation rooted in U.S. military transport programs, and today it is used interchangeably with “shipping container,” “sea container,” and “cargo container.”
Most Conex boxes are constructed from Corten steel, a corrosion-resistant alloy that gives the structure long-term strength. That structural integrity is exactly why the format works so well as a starting shell for customization: the box is already engineered to be secure, stackable, and durable before a single modification is made.
A “custom” Conex box simply means a standard container that has been modified with added features—doors, windows, insulation, wiring, or interior walls—to serve a purpose beyond basic cargo storage.
Conex Box Sizes and Dimensions
Custom Conex boxes start from standard ISO footprints. The table below outlines the common lengths and approximate interior specifications used as the base for most custom projects.
| Size | Common Interior Dimensions (approx.) | Typical Use |
| 10 foot Shipping Container | ~9’4″ L × 7’8″ W × 7’10” H | Guard shacks, compact storage, ticket booths |
| 20 foot Shipping Comtainer | ~19’4″ L × 7’9″ W × 7’10” H | Offices, half office/half storage, retail, general storage |
| 40 foot Shipping Container | ~39’5″ L × 7’8″ W × 7’10” H | Large offices, open-bay workspaces, warehouse-style storage |
| 40 foot High Cube Container | ~39’5″ L × 7’8″ W × 8’10” H | Extra vertical clearance for equipment, retail, and workspaces |
The 20-foot Shipping container remains the most requested size because it balances usable floor space with a compact footprint. The 40-foot High Cube adds roughly a foot of interior height, which matters for retail conversions, offices, and any build where equipment or shelving needs headroom.
What Can a Custom Conex Box Be Modified Into?
One of the defining strengths of the CONEX format is how many finished products a single steel shell can become. Below are common custom configurations built on standard containers.
| Configuration | What It Is |
| Office container | Insulated, wired workspace with lighting, climate control, and a walk-in door |
| Concession stand | Serving container with a service window, counter, and interior prep space |
| Guard shack | Compact 10-foot booth for site security and access control |
| Car storage container | Reinforced unit sized to hold vehicles for collectors or dealers |
| Break room | Enclosed, climate-controlled space for on-site crews |
| Security office | Monitored workspace with windows and a secured entry |
| Ticket booth | Small-footprint sales or entry-point structure for events and venues |
| Full side-open container | Cargo doors that open the full length of one side for wide-load access |
Common Custom Modifications Explained
Custom CONEX boxes are built by combining individual modifications. Understanding each option makes it easier to spec a container that fits your project.
- Doors: Options include standard cargo (swing) doors, roll-up doors, walk-in personnel doors, and industrial man doors. A single container can combine multiple door types—for example, a roll-up door for access and a walk-in door for daily entry.
- Windows: Windows can be added for offices, concession service, ventilation, or visibility in guard and security builds. Placement and size are specified in the layout.
- Insulation: Insulation packages line the interior for temperature control, making a container suitable for offices, break rooms, and workspaces where crews spend the day.
- Electrical package: Custom units can include lighting, outlets, panels, HVAC/air conditioning, and full wiring so the container functions as a ready workspace on arrival at the job site.
- Interior partitions: Multi-purpose floor plans—such as a 20-foot half office/half storage layout or a 40-foot open bay—divide the interior to serve two functions in one box.
- Flooring and security: Marine plywood flooring provides a durable work surface, and a secured lockbox can be installed to protect the cargo doors.
How do businesses use custom Conex Boxes?
Custom CONEX boxes serve a wide range of industries because the same steel shell adapts to storage, workspace, and point-of-service roles.
- Construction and job sites use custom containers as on-site offices Containers, secure tool storage, and break rooms that keep crews and equipment in one place.
- Retail and events convert containers into pop-up shops, concession stands, and ticket booths, taking advantage of the container’s secure, self-contained footprint.
- Automotive buyers use reinforced car-storage containers to hold vehicles for collectors, restorers, and dealerships.
- Government and institutional clients—including municipalities, utilities, and public agencies—rely on custom containers for guard shacks, security offices, and field storage. Aztec Container has supplied organizations such as the City of Carlsbad, LADWP, and California State Parks, among others.
- Healthcare and services adapt office containers into mobile clinics and field offices outfitted with insulation, electrical power, and ground-level access.
New vs. Used CONEX Boxes for Custom Builds
Both new and used containers can serve as the base for a custom build, and the right choice depends on budget and finish expectations.
- New (one-trip) containers arrive in near-original condition with minimal wear, making them a strong base for offices, retail conversions, and any build where appearance matters.
- Used containers are more economical and remain structurally sound for storage, job-site units, and utilitarian workspaces. They may show cosmetic wear from prior cargo use.
For customer-facing builds like concession stands or retail shops, many buyers choose a newer base so the finished unit looks polished. For back-of-house storage or field offices, a quality used container often delivers the same function at a lower cost.
Buying vs. Renting a Custom CONEX Box
Whether to buy or rent depends on how long the container is needed and how specialized the build is.
- Buying makes sense for permanent installations, heavily customized units, and long-term use where the container becomes a fixed asset. Aztec Container offers sales nationwide.
- Renting suits temporary projects, seasonal needs, and shorter-term job sites. Aztec Container offers rentals within California.
Highly specialized custom builds—such as a branded concession stand or a purpose-built office layout—are more commonly purchased, since the modifications are tailored to a specific operation.
Why the Conex Format Works for Custom Projects
The CONEX box succeeds as a custom-built platform for three structural reasons. First, it is manufactured to ISO standards, so every unit shares a predictable, stackable footprint. Second, its Corten steel construction provides a secure, durable shell before any modification begins. Third, the format is modular by nature—doors, windows, insulation, and partitions can be added in almost any combination.
The result is a single, standardized starting point that can become an office, a shop, a booth, or a secure storage unit. That flexibility, combined with more than five decades of container experience at Aztec Container since 1969, is why the CONEX box remains a go-to solution for businesses that need a purpose-built steel structure.
Frequently Asked Questions
What does Conex actually stand for?
CONEX is short for “Container Express,” a term that originated in U.S. military logistics for standardized steel shipping containers. Today, people use “CONEX box,” “shipping container,” and “sea container” to mean the same thing.
Is a Conex box the same as a shipping container?
Yes. “CONEX box” is another name for a steel ISO shipping container. The terms are used interchangeably in the industry, so a custom CONEX box is simply a customized shipping container.
What sizes do custom Conex boxes come in?
The common lengths are 10, 20, 40, and 45 feet, with 40-foot and 45-foot units also available in a taller High Cube height. The 20-foot size is the most popular because it balances usable space with a compact footprint.
Can a Conex box be turned into an office?
Yes. Office conversions typically add insulation, an electrical package with lighting and air conditioning, windows, and a walk-in door. Layouts range from a full office to a split half office/half storage design.
What kinds of doors can be added to a custom container?
Options include standard cargo swing doors, roll-up doors, walk-in personnel doors, and industrial man doors. A single container can combine more than one door type depending on how it will be used.
How much does a custom Conex box cost?
There is no fixed price—cost depends on size, whether the container is new or used, the modifications selected, and the configuration. Defining the intended use first is the best way to get an accurate quote.
Should I choose a new or used container for a custom build?
New (one-trip) containers are ideal when appearance matters, such as retail or concession builds. Used containers are more economical and work well for storage and job-site units where cosmetic wear isn’t a concern.
Can I rent a custom Conex box instead of buying?
Yes. Aztec Container offers rentals in California and sales nationwide. Renting suits temporary and seasonal needs, while heavily customized units are more often purchased for long-term use.
What can a 10-foot Conex box be used for?
Its compact footprint makes it well suited to guard shacks, ticket booths, and small-scale storage. It’s the go-to size when floor space is limited, but a secure steel structure is still needed.
Who uses custom Conex boxes?
Construction firms, retailers, event organizers, automotive businesses, healthcare providers, and government agencies all use them—for offices, shops, concession stands, security booths, car storage, and field workspaces.