Tracking · practical guide

How to track a container by number, without knowing which carrier it belongs to

September 21, 2026 · 7 min read · Flettia team

If you have a container on the water, you almost always have one piece of data at hand: its number. That is enough. The number almost always tells you which carrier owns the box, and with the carrier you can find out where it is, when it arrives and which moves it has made. This guide explains how to read that number, how to track it in one place instead of visiting every carrier's portal, and what to look for in the timeline so you don't pay demurrage.

All you need: the container number

A container number always has the same shape, defined by ISO 6346: four letters and seven digits, for example MSCU1234566. The first three letters identify the owner of the equipment, the fourth is the category (U for freight containers), then six serial digits, and finally a check digit. That last digit is computed from the other ten, so a mistyped number is caught before any lookup.

Where does it appear? On the bill of lading (BL), in the carrier's booking confirmation, on the packing list and in the shipping advice your freight forwarder sends. If all you have is the BL number, look for the “Container No.” field on that same document: the containers of that shipment are listed there. Flettia's tracker works by container number today; the BL is not a search key yet.

The four letters usually tell you the carrier

The owner prefix is a code registered with the BIC (Bureau International des Containers). When the carrier owns the box, the prefix says so and you don't need to know the line. Many boxes are leased and carry the lessor's code instead (TCLU, TCNU and others), which doesn't reveal the line; for those, the tracker asks the carriers that allow it: today MSC, COSCO, Hapag-Lloyd, ONE, Evergreen, Yang Ming and PIL. These are the carrier-owned prefixes you will see most often on the lines the tracker covers:

Maersk: MRKU, MSKU, MAEU, MRSU, MNBU, PONU. Sealand and Hamburg Süd (SUDU) are Maersk group brands and are looked up in the same system.
MSC: MSCU, MEDU, MSDU.
COSCO: COSU, CSNU, CBHU. OOCL: OOLU, OOCU. Same group, and their data comes from the same system.
Hapag-Lloyd: HLCU, HLXU, HLBU, plus the ones inherited from UASC: UACU, UASU.
ONE (Ocean Network Express): ONEU.
Evergreen: EGHU, EISU, EGSU, EMCU, EITU.
Yang Ming: YMLU, YMMU.
PIL (Pacific International Lines): PCIU, PILU.

Step by step: track in one place

The traditional route is to open each carrier's portal, and every portal asks for data differently and names events differently. Flettia's tracker runs one search for the carriers it covers and shows the result in a single view.

Go to tracker.flettia.com and type the full container number, all eleven characters. If the check digit doesn't add up, it tells you immediately.
The tracker infers the carrier from the prefix, or asks the carriers when the box is leased, and queries its data. You never pick the line.
You see the route on a map, the current status (at origin, in transit, discharged at destination, delivered or empty returned), the estimated or actual arrival date at the final port, and the timeline of milestones.
Every milestone is shown under the same name whichever carrier it comes from: empty pickup, gate in, loaded on board, departure, arrival, discharge, gate out and empty return.

How to read the timeline

Events with a past date are actual: the carrier has already recorded them. Future events are estimates published by each carrier; they change when the vessel's schedule changes, and no tracker can promise an estimate will hold. What is useful is seeing when the estimate moved and by how much.

A voyage with transshipment shows two departures and two arrivals: the container comes off one vessel at an intermediate port and goes onto another. That is normal, and it is also where dates slip the most, because the connection depends on the second vessel being on time.

Each carrier reports the location of an event in its own way: some send the port's UN/LOCODE, others a free-text name. The tracker translates all of them into one format so the timeline reads the same in every case.

Free days, demurrage and detention: what to watch

The hidden cost of a container is not the freight: it is the days. After discharge at the destination port, the carrier's free days start running for you to pick the container up from the terminal; once they run out, demurrage is charged for every additional day. After pickup, another clock runs for returning the empty to the depot; past that deadline, detention is charged. Free time and rates depend on your contract with each carrier and on the port.

That is why two dates on the timeline matter more than any other: discharge, which is usually where free days start counting, and gate out, which confirms the container is now with the trucker. Seeing those dates the same day they happen is what lets you schedule the pickup before charges begin.

What Flettia's tracker does and doesn't do today

It covers the major carriers: COSCO, OOCL, MSC, Maersk, Sealand, Hamburg Süd, Hapag-Lloyd, ONE, Yang Ming, Evergreen and PIL. If your container belongs to another line, that carrier's portal is still the way.
It searches by container number. Search by BL is not available yet.
For leased boxes (TCLU, TCNU…) it asks MSC, COSCO, Hapag-Lloyd, ONE, Evergreen, Yang Ming and PIL. A leased box travelling with Maersk isn't found on its own yet.
It shows the data the carrier publishes; estimated dates are the carrier's and can change.
It works for imports and exports alike: tracking follows the container, not the direction of the trip.

For freight forwarders: tracking as part of the file

For an importer, tracking is a lookup. For a freight forwarder it is a task repeated dozens of times a week, once per container per customer. That follow-up is one of the jobs Flettia hands to an AI employee inside each operation's file, with the usual rules: the agent watches and alerts, and a person decides what to do with the alert. The public tracker is that same lookup, open to anyone with a container number at hand.

Guides by carrier

Each carrier publishes its data its own way. These short guides sum up what is specific to each one: prefixes, what it publishes and what to watch.

Frequently asked questions

Do I need to know which carrier owns the container?

No. When the carrier owns the box, the four letters of the number say so. When it is leased, the tracker asks the carriers that allow it.

Can I track with the BL number?

Not today. Use the container number, which appears on the BL itself in the “Container No.” field; our bill of lading tracking guide walks through it.

Why does the estimated arrival date change?

The carrier publishes it from the vessel's schedule and updates it on delays, rotation changes or missed transshipments. The tracker shows the latest published estimate.

What is the difference between “discharged at destination” and “delivered”?

Discharged means the container came off the vessel and is at the terminal; free days usually start counting there. Delivered means it has left the terminal for its final destination.

Does it work for exports?

Yes. Tracking follows the container in either direction, as long as the carrier is among those covered.

Is it free?

The first search is free and requires no sign-up.

Sources

Track your container now

Your first search is free, no sign-up. Type the number and we tell you where it is going: route on a map, status, arrival date and every move.

Open the tracker