Free container tracking: validate the number against its ISO 6346 check digit, see which line owns the box, and go straight to that carrier's tracking screen. Container tracking works by matching an 11-character ISO 6346 number against the events that carriers, terminals and depots record as the box moves. The position on your screen usually doesn't come from a device inside the container — it is assembled from gate moves, load and discharge records, and the vessel's own position. Some carriers have begun fitting telematics units, but standard tracking screens still run on recorded events. That makes tracking an event-by-event timeline rather than a continuous signal, which is why a status can sit unchanged for days and still be correct. Below: how to read the number, what each milestone means, and which milestone starts the free-time clocks behind demurrage and detention.
You enter the 11-character number and three things happen locally, in a fraction of a second: the format is checked, the ISO 6346 check digit is recalculated from the first ten characters, and the owner prefix is matched against the lines and leasing companies that use it. What you get back is a verdict on the number itself plus the right place to run it — the carrier's own tracking screen, where the actual events are recorded.
The prefix identifies the owner of the steel box, and ownership is not the same thing as the carrier on your booking. Lines own large fleets, but they also lease heavily, and a leased box can sail with a different line on every voyage. That is why a prefix like TCLU or CAIU is an honest dead end for carrier identification — the answer is in your booking confirmation, not on the door of the container.
A container number is 11 characters: four letters followed by seven digits. The first three letters are the owner code registered with the BIC (Bureau International des Containers et du Transport Intermodal), the registration authority for ISO 6346; the fourth letter is the equipment category, which is U for freight containers. Then comes a six-digit serial number and a check digit calculated from the first ten characters. The letters identify the owner, not the carrier: a large share of boxes belongs to leasing companies and sails with whichever line hired them.
A container number tracks one box, a bill of lading number tracks every box on that B/L, and a booking number is what you have before equipment is assigned. If you shipped through a freight forwarder or NVOCC, the house bill of lading (HBL) in your file usually returns nothing on the carrier's system — the line only recognises the master bill of lading (MBL) it issued and the container numbers under it. Before searching, confirm two things from the booking confirmation, arrival notice or B/L: the container number and the name of the actual ocean carrier.
Every line in a tracking history is an event someone recorded — at a terminal gate, during vessel operations, or at a depot. Most containers carry no positioning device, so sea positions generally come from the vessel and inland moves from gate records. Lines describe the same event in different words; industry work on a shared event vocabulary is under way, but naming still varies from carrier to carrier. Timestamps are usually local port time, and an event can appear in the system hours after it physically happened.
Demurrage runs while the box sits inside the terminal; detention runs while it is out in your control — and tracking events are what trigger both. In practice demurrage free time starts at discharge from the vessel and stops when the box passes the gate outbound; detention starts at that same gate-out and stops when the empty is returned to the depot. Free time depends on the port, the line and your contract, and some carriers run a single merged clock instead of two. The date to watch is therefore not the ETA but the discharge date and the last free day.
A status that hasn't changed in days is rarely a broken feed — it is usually a step waiting to happen. The most common causes are a rollover to a later sailing, a wait for the connecting vessel at a transshipment hub, and berth or yard congestion at the port. Before loading, a missing VGM or incomplete paperwork keeps the box at the terminal; at destination, a customs hold or a carrier release block — unpaid freight included — stops it after discharge. If the search returns nothing at all, check the number and the carrier first, then whether the box has been gated in yet.
A very common reason a search fails is the number itself — a digit typed in the letter block, or a letter typed in the digit block. Once results do appear, the expensive mistake is reading the ETA as the date the cargo can be collected; discharge, clearance and a terminal appointment can add days after the ship arrives. A tracking screen is commercial information — it is neither the transport document nor a document of title; the bill of lading and the delivery documents are what count. If you follow many boxes at once, link container numbers to the shipment record itself — in a transport management system, or in a single shared tracking list — instead of repeating the daily round of carrier portals.
Enter the 11-character number printed on the box (4 letters + 7 digits). This page validates it against the ISO 6346 check digit, tells you from the prefix which line or leasing company owns the box, and links you straight to that carrier's own tracking screen. Voyage events — load, transshipment, discharge, demurrage clocks — live in the carrier's system, so that is where your number returns a real record.
It is printed on the door, the side wall and the roof of the box, and it appears on the bill of lading and the booking confirmation. The structure is fixed: three letters for the owner code, a fourth letter for the equipment category (U for freight containers), six digits of serial number and one check digit — for example MSCU 123456 6.
The last digit is a check digit computed from the first ten characters: each character value is multiplied by successive powers of two, the sum is taken modulo 11, and a result of 10 is written as 0. This page runs that calculation for you — if it does not match, one character has been mistyped and the carrier's own screen will not find it either.
Only partly. The first four characters identify the OWNER of the box, not the carrier on that particular voyage. If the owner is a shipping line (MSCU, MAEU, CMAU, COSU, HLCU and so on) the number gives you the line directly. If the owner is a leasing company (TCLU, CAIU, TEMU …) the box is used by many lines and the carrier cannot be derived from the number — check the booking confirmation or the bill of lading instead.
Each line runs its own tracking screen and that is the single source of truth for event data. When you enter your number here the prefix is matched to the line and you get a link to its tracking page; if the prefix is not recognised you can pick from the directory of major carriers' tracking screens.
It is free; no email and no account are needed to validate a number and identify the line.
They are two separate clocks running in two different places. Demurrage runs while the full container sits inside the terminal: free time starts at discharge from the vessel and stops when the box leaves the gate. Detention runs while the box is in your control: it starts at that same gate-out and stops when the empty is returned to the depot. The same delay is billed under one or the other, not both — and the gate-out record in your tracking history is what decides which. Some carriers merge the two into a single combined clock, so confirm which model your contract uses.
First the spelling (four letters plus seven digits), then the carrier, then whether the box has been gated in — most systems have no events before that. If the number you hold is a house bill of lading, as a rule it will not resolve on the ocean carrier's portal; ask your forwarder to trace it against the master B/L. Carriers also archive records some time after delivery, so closed shipments may simply return nothing.
The number belongs to the box, not to your cargo. Once the empty is returned it is allocated to another customer, and the system shows the most recent voyage. To keep a permanent history of your own shipment, work from the bill of lading or booking number and the dates in your own records.
No. Free time runs on actual events, not estimates: the vessel's actual discharge for demurrage, and the gate-out for detention. Use the ETA for planning, but confirm the last free day from the carrier or terminal record.
Standard tracking screens do not show that; the event log is about the movement of the box. Live temperature, humidity or door data requires telematics-equipped equipment or a carrier's reefer monitoring service. Even without telematics, the reefer unit logs temperature in its own controller, and you can request that record from the carrier after the voyage. For temperature-controlled cargo, agree both at booking rather than after departure.
Search by master B/L or booking number, which lists every container under the same bill of lading. Each box still has its own event history, though — one container can be rolled and end up a sailing behind the rest, so spot-check individual numbers on critical shipments.
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