Container inventory management means knowing, for every box you own or lease, where it is, whether it is empty or full, what condition it is in and what it is costing you. For a shipping line serving U.S. ports it also means reporting some of those movements to CBP. This guide covers the identifiers, events, documents and daily habits that keep the count right.
For a small shipping line or NVOCC operating its own equipment, the container fleet is one of the largest costs on the books, and every unit sits in one of a few states: empty and available, assigned to a booking, out with a shipper or consignee, full at a terminal, on board, under repair or off-hire. Inventory management is the discipline of knowing that state for every unit at any moment, and of making sure each change is recorded by the person who saw it happen.
When the count is wrong, the symptoms are expensive: bookings accepted with no equipment to fill them, empties repositioned to the wrong port, per diem paid on boxes nobody can find, and repair claims that cannot be proven.
The starting point is the container number. The Bureau International des Containers (BIC) describes the identification number as an owner prefix of three capital letters, a single equipment category identifier, a six-digit serial number and a check digit that helps verify the owner code and serial number when they are recorded or transmitted (BIC: identification number). The category letter is U for freight containers, J for detachable freight container-related equipment and Z for trailers and chassis.
Equipment type comes from the size and type code. Under the BIC tables, the first character gives the length, the second the height and the last two the type (BIC: size and type code).
| Code | Length | Height | Type |
|---|---|---|---|
| 22G1 | 20 ft | 8 ft 6 in | General purpose |
| 42G1 | 40 ft | 8 ft 6 in | General purpose |
| 45G1 | 40 ft | 9 ft 6 in (high cube) | General purpose |
| 45R1 | 40 ft | 9 ft 6 in (high cube) | Refrigerated |
Software should validate the check digit every time a number is typed or received, because one transposed digit creates a phantom container and hides a real one.
A container’s status changes at a predictable set of events, and CBP’s own list is a good template. 19 CFR 4.7d names these events for containers destined to arrive at a U.S. port by vessel: booking confirmed, terminal gate inspection, arrival at or departure from a facility (gate-in and gate-out), loading on or unloading from a conveyance, vessel departure or arrival, intra-terminal movement, ordered stuffed or stripped, confirmed stuffed or stripped, and stopped for heavy repair.
| Event | Typical document or record | Inventory effect |
|---|---|---|
| Booking confirmed | Booking | Unit reserved, still empty |
| Gate out empty to shipper | Equipment interchange receipt (EIR) | Unit out, responsibility transferred |
| Gate in full | EIR | Unit full at terminal, condition recorded |
| Stuffed or stripped | Stuffing or stripping record, dock receipt | Status changes full or empty |
| Loaded or discharged | Load and discharge lists, stow plan | Unit on board or at the port of discharge |
| Stopped for repair | Repair estimate | Unit unavailable until released |
Under 19 CFR 4.7d, if a carrier creates or collects a container status message in its equipment tracking system for one of the events above, it must transmit that message to CBP no later than 24 hours after it is entered into the system. Each message must include the event code as defined in the ANSI X12 or UN EDIFACT standards, the container number, the date and time of the event, whether the container is empty or full, the location, and the vessel if the container is associated with one.
Separately, 19 CFR 4.7c requires the vessel stow plan no later than 48 hours after the vessel departs the last foreign port, or before arrival at the first U.S. port for voyages shorter than 48 hours. For each container it lists the container operator, equipment number, size and type, stow position, hazmat code if applicable and port of lading, among other items.
The practical point: if your inventory data is clean, these reports come out of it. If it is not, you are correcting the same errors twice, once for yourself and once for CBP. Check the current rules with CBP before relying on any summary.
The equipment interchange receipt is where responsibility for a box changes hands, so it should record the container and chassis numbers, seal, empty or full status, and condition at every gate move. Terminals increasingly report these moves electronically. The SMDG user group publishes EDIFACT implementation guides for container messages such as CODECO for gate-in and gate-out confirmation and COPRAR and COARRI for vessel discharge and loading orders and confirmations (SMDG container messages). Our article on EDIFACT vs ANSI X12 explains how those messages compare with U.S. standards.
Most small lines mix owned and leased equipment. Each leased unit carries on-hire and off-hire dates, a daily rate and return conditions, so inventory reports should separate owned from leased and show days on hire. Repairs belong in the same record: an estimate, an approval, the cost, and whether the cost is recoverable from the party that held the box when the damage was noted on the EIR. Demurrage and detention follow the same logic on the customer side, and they are only billable if the gate dates are right.
In GDZ-ISIS, the Equipment Control Module is updated by every traffic module and tracks movement, status, seals, temperature, holds and history, with reports such as depot holdings, leasing and repair history. Whatever system you use, the rule is the same: the event and the inventory update should be a single step. If you want to compare approaches, talk to our team.
It has a three-letter owner code, one equipment category letter (U for freight containers), a six-digit serial number and a check digit that verifies the rest, as described by the Bureau International des Containers.
Under the BIC size and type tables, 4 is 40 feet long, 5 is 9 feet 6 inches high (high cube) and G1 is general purpose, so 45G1 is a 40-foot high-cube dry container.
Under 19 CFR 4.7d, if a carrier creates or collects a container status message for listed events on U.S.-bound containers, it must send it to CBP within 24 hours of entering it in its equipment tracking system. Confirm current requirements with CBP.
An EIR records a container handover at a gate or depot: unit and chassis numbers, seal, empty or full status and condition. It establishes who held the unit and in what condition, which matters for damage and per diem disputes.
Gate moves should be recorded daily, and many carriers reconcile their records against terminal and depot reports weekly. Units with no recent movement deserve a regular review so they do not quietly accrue charges.