MMSI Lookup: How to Find a Ship’s MMSI Number
In this article 8 sections
An MMSI lookup answers one of two questions: you have a nine-digit number and want to know which ship it belongs to, or you have a ship and want its number. Both directions run through the same system. There is no central phone book you can search by name the way you would a company registry. MMSI stands for Maritime Mobile Service Identity, and the number exists so radios and tracking systems can identify a vessel automatically, without a human reading a name off a hull. This guide covers what the nine digits encode, how to run a lookup against a live position, and the two situations where a search comes back empty even though the number typed in was correct.
What an MMSI Number Actually Is
Every ship’s radio has a nine-digit name tag called an MMSI. It was built for Digital Selective Calling, the system that lets a VHF or MF/HF radio send a distress alert naming the vessel in trouble without anyone saying a word. AIS simply borrowed the same number, which is why a tracking map can search on it.
Reading the nine digits
Split it as 3 + 6. The first three digits (the MID) show which country issued the number, and the last six are a serial from that country’s regulator. For example, 366 to 369 is the US, 232 to 235 is the UK, 431 or 432 is Japan, and 412 or 413 is China.
This only tells you where the paperwork started. It says nothing about where the ship is now or who owns it, and a vessel can spend its whole life at sea without ever visiting the country in its MMSI.
MMSI vs. IMO
People mix these up all the time:
- IMO number: seven digits, tied to the hull itself. It stays the same for the ship’s entire life, whatever happens to its name, flag, or owner.
- MMSI: nine digits, tied to the radio and AIS transponder. Reflag the ship or re-register it, and the MMSI changes.
Think of the IMO as the ship’s fingerprint, and the MMSI as a phone number that changes when it moves to a new carrier.
Why People Search for an MMSI Number
Most searches split into two groups with almost nothing in common. The first is someone who already has the nine digits, from a distress call, a shipment record or a photograph of a hull, and wants to confirm which vessel they belong to and where it is now. The second is a vessel owner who has just fitted a VHF radio with DSC and needs a number assigned before the set is any use in an emergency.
A lookup tool only ever serves the first group.
There is a narrower third case. Container lines run near-identical names across whole vessel classes, and a search on a shipping line’s own CMA CGM tracking page often hands you an MMSI precisely because the ship’s name alone was not specific enough.
How to Look Up a Ship's MMSI Number, Step by Step
Step 1: Confirm you have all nine digits
A ship MMSI never starts with a zero and is always nine digits long. Shorter, longer, or leading-zero numbers belong to a different category, covered further down. Copy it exactly. A single transposed digit returns nothing, or worse, the wrong ship entirely.
Step 2: Open MarineRadar and use the vessel search
Type the nine digits into the search bar the same way you would search a vessel by name. MarineRadar matches AIS identifiers as well as names, and a correctly typed MMSI resolves to a vessel profile as long as that station has transmitted recently enough to be in the system.
Step 3: Check the MID against what you expected
Glance at the first three digits before trusting anything else on the page. Told it was a Panamanian-flagged bulker, but the MID reads European? You likely have the wrong number, or the ship has been reflagged since your source was current.
Step 4: Read the vessel profile
Once resolved, the profile carries the ship’s name, IMO number, flag, type, dimensions, and its current position, speed and course. A nine-digit code most people have never seen turns into a moving dot with a destination and an ETA.
Step 5: Save it rather than re-typing it
Add the vessel to a saved list if you will want it again. Doing this for several ships at once gets old fast one search at a time, and grouping them properly is its own guide.
What an MMSI Lookup Cannot Tell You
A lookup only works if the station has broadcast recently enough for a receiver to catch it, and coverage matters more than people expect. A brand-new MMSI, sitting in a radio that has never left the shop, resolves to nothing. It exists in a regulator’s records before it exists on any map, and a vessel deep in open ocean depends on satellite AIS coverage rather than a shore station, where passes update far less often than a busy port does.
A stale position rather than nothing at all is usually this, not a fault in your search. Switch a transponder off, deliberately or through a failure, and the MMSI you typed correctly still shows nothing.
MMSI Formats Beyond a Standard Ship
Most searches involve an ordinary ship station. The same nine-digit space is carved up for other kinds of transmitter, and the pattern explains why some numbers behave differently.
| Format | Pattern | What it identifies |
|---|---|---|
| Ship station | MIDxxxxxx | An individual vessel, never starts with 0 |
| Group ship call | 0MIDxxxxx | A fleet sharing one call, single leading zero |
| Coast station | 00MIDxxxx | A shore-based radio station, double leading zero |
| SAR aircraft | 111MIDxxx | Search-and-rescue aircraft, not a surface vessel |
| AIS aid to navigation | 99MIDxxxx | A fixed or floating marker, such as a buoy |
That last row catches people out the most. A stationary AIS target at the mouth of a channel is often a navigation aid, not an anchored ship sitting still for a suspiciously long time. The format gives it away before you need to guess.
Some tracking tools let you filter results by these formats directly, which is worth knowing if you are scanning a busy strait and want ships only, not the aids to navigation marking the channel edges. Filtering out coast stations and buoys before you start narrows a crowded chart to the traffic that is actually moving.
Does an MMSI Change When a Vessel Is Sold?
Not automatically. An MMSI is registered to the equipment and its owner, not welded to the hull the way an IMO number is. Sell a vessel and skip the deregistration step, and the number keeps broadcasting under the previous owner’s name and contact details. A lookup then returns an accurate position tied to an inaccurate registration. Confirm the transfer, or apply fresh, before trusting an inherited MMSI for distress calling.
Common Reasons a Search Comes Back Empty
Four causes account for nearly every failed lookup:
- A mistyped digit, usually a transposed pair that still looks plausible.
- A vessel that has not transmitted recently, whether from a powered-down transponder, an equipment fault, or simply being out of receiver range.
- A number that belongs to a coast station, navigation aid or SAR aircraft rather than a ship, typed into a ship-only search.
- An MMSI so newly issued it has never been programmed into a live transmitter at all.
Work through those in order before assuming the tracking system itself is broken.
The Number Matters Beyond Tracking
An MMSI makes a distress call specific rather than general. Pressing a DSC distress button sends the vessel’s own MMSI automatically, so a rescue coordination centre knows immediately which vessel is in trouble, and roughly where if the set has a GPS connection, while every compatible radio within range gets the same alert carrying the same identifying number. The same identifier reappears on the AIS side through the Class A and Class B AIS transponders fitted to commercial and recreational vessels. One number, two systems.
How the Broadcast Reaches a Map
Nothing about an MMSI matters until something picks up the broadcast. Coastal stations, satellites and increasingly other ships all relay the same messages into the systems ship tracking apps receive vessel data from. The MMSI is a small field in that message next to position and speed, but every one of those systems keys on it to avoid confusing one hull with another.
Conclusion
An MMSI lookup works in one direction: from a correct, currently broadcasting nine-digit number to the ship carrying it. It will not issue you a new number, and it will not find a vessel that has never transmitted or sits out of range right now. Within that limit it is fast, free, and more reliable than guessing from a name alone, especially in a fleet where several hulls share one.
MarineRadar is free to start on Android and iPhone. Type a nine-digit MMSI into the search bar, and if the vessel is transmitting, its live position appears within seconds.
FAQs
What is an MMSI number?
A nine-digit code assigned to a vessel’s radio and AIS equipment. It is used for Digital Selective Calling distress alerts and for finding the vessel on a live tracking map. The first three digits identify the issuing country.
How do I find my vessel's MMSI number?
Request one from your national telecommunications or maritime authority, such as the FCC or BoatUS in the United States, or Ofcom in the United Kingdom, when you register a DSC-equipped radio. No tracking app can issue one.
Does an MMSI number stay with a vessel when it's sold?
Not unless someone updates the registration. Confirm the transfer or apply fresh.
What is the difference between an MMSI and an IMO number?
An IMO number is seven digits and stays with a hull for life. An MMSI is nine digits, tied to the radio and AIS equipment, and changes if the vessel is reflagged or re-registered.
Can I look up any ship's MMSI for free?
Yes, on MarineRadar, as long as the vessel is currently transmitting AIS within range of a receiver.
Why does my MMSI lookup return nothing?
Usually one of four things: a mistyped digit, a vessel that is not currently broadcasting, a number that belongs to a coast station or navigation aid rather than a ship, or a newly issued MMSI never programmed into a live transmitter yet.
What do the first three digits of an MMSI mean?
The Maritime Identification Digits, naming the country that issued the number. 366 through 369 is the United States. 232 through 235 is the United Kingdom.
Track the ships behind the story
MarineRadar follows 112,000+ vessels with satellite positions every 5 minutes. Search by name, MMSI or IMO — free on iOS and Android.
