ICCID number explained: the SIM serial, digit by digit
Short answer: An ICCID is the serial number of a SIM card or eSIM profile: usually 19 or 20 digits, starting with 89, printed on the card and readable from the device. It identifies the SIM itself, while the IMSI identifies the subscription on the network and the IMEI identifies the phone or module.
The ICCID number explained: what the SIM serial is, how its digits break down, how it differs from IMSI and IMEI, and where to find it on phones and modules.
This article covers what the ICCID is, what each group of digits means, how it relates to IMSI, IMEI and EID, where to find it, and why IoT fleets keep track of it. It does not cover SIM file systems in detail, the authentication algorithms, or how any particular operator formats its numbers.
An ICCID number is the serial number of a SIM. The letters stand for Integrated Circuit Card Identifier. The number is usually 19 or 20 digits long, always starts with 89, and is both printed on the card and stored on the chip. It names the SIM itself, which makes it a different thing from the IMSI, the identity the mobile network uses for the subscription, and from the IMEI, the identity of the phone or cellular module the SIM sits in. This article breaks the number into its fields, sets it beside the other identifiers, shows where to read it on a phone and on an IoT module, and explains why anyone running a fleet of cellular devices ends up keeping a record keyed on it.
What an ICCID number is
The ICCID is defined in ITU-T Recommendation E.118, which covers numbering for telecommunication charge cards. Its layout borrows the card-numbering scheme of ISO/IEC 7812, the same scheme that gives bank cards their structure: a prefix that says what industry the card belongs to, an identifier for the issuer, an account number, and a check digit at the end.
The number is assigned when the SIM is manufactured and personalized for an operator. It is written into a file on the chip and printed or laser-engraved on the card body, usually with a barcode on the plastic carrier as well. It does not change for the life of the card. Changing tariff, topping up or moving the SIM to another device leaves the ICCID alone; a new SIM means a new ICCID.
The ICCID is an identifier, and knowing it does not let anyone copy the SIM. What authenticates a SIM to the network is a secret key stored on the chip that cannot be read out. The ICCID is still worth handling with some care, because it is the number an operator or connectivity platform uses to find, activate and suspend a particular card.
The structure of an ICCID
An ICCID has five parts, read from the left.
The first two digits are the major industry identifier, and for SIMs they are always 89, the value ISO/IEC 7812 gives to telecommunications. Next comes a country code of one to three digits, based on the international calling code from ITU-T E.164. Then an issuer identifier, a short number for the operator that issued the card, often matching its mobile network code. Then the individual account number, which is the card’s own serial within that issuer’s range; its length varies between issuers but is fixed for any one issuer. The last digit is usually a check digit.
The check digit is calculated with the Luhn formula, the same one used on bank cards. Starting from the right, every second digit is doubled, the digits of the results are added up with the rest, and the check digit is whatever brings the total to a multiple of ten. It catches any single mistyped digit and most swaps of two neighboring digits, which is useful when people copy ICCIDs by hand from a label into a spreadsheet.
Why the length varies
E.118 allows an ICCID of up to 19 digits including the check digit. The SIM, however, stores the ICCID in a field ten bytes long, which holds 20 digits, and many issuers use all 20. So both lengths are common, and a system that stores ICCIDs should accept either. On the chip the digits are packed two to a byte with the pair swapped, and a 19-digit number is padded with a filler value, which is why a raw read of the file looks scrambled until it is decoded. Some tools and labels also split the number into groups or drop the check digit, so compare numbers as digit strings with the spaces removed and be wary of a match that is one digit short.
ICCID vs IMSI vs IMEI, and the EID
Four identifiers turn up around a cellular device, and each belongs to a different thing.
| Identifier | Identifies | Typical length | Stored in | Changes when |
|---|---|---|---|---|
| ICCID | The SIM card, or one profile on an eSIM | Usually 19 or 20 digits, starting 89 | The SIM, and printed on the card | A new SIM or a new eSIM profile |
| IMSI | The subscription the network sees | Up to 15 digits: country code, network code, subscriber number | The SIM | A new SIM or profile, or a multi-IMSI SIM switching identity |
| IMEI | The phone or cellular module | 15 digits, the last a check digit | The device or module | Never, for a given device |
| EID | The eUICC chip that holds eSIM profiles | 32 digits | The eUICC | Never, for a given chip |
The IMSI, International Mobile Subscriber Identity, is what the network uses. It starts with a three-digit mobile country code and a two- or three-digit mobile network code, which is how a network knows whose subscriber it is looking at and whether it has a roaming agreement for them. The network authenticates the IMSI using the secret key on the SIM. Because the IMSI identifies a subscriber, networks send it over the air as little as possible and use temporary identities instead, and 5G goes further by sending it only in concealed form.
The IMEI, International Mobile Equipment Identity, belongs to the hardware. It is set by the device or module maker and identifies the radio, whichever SIM is inside. Networks can read it and check it against lists of blocked devices.
The ICCID sits between the two. It is the label on the card, and it is how the business side of the connection (the operator’s systems, the connectivity platform, the invoice) refers to a SIM. The EID only exists on eSIM hardware, and it is covered below.
Where to find the ICCID number
On the SIM card
The ICCID is printed on the SIM itself and on the larger plastic card it was snapped out of, often in groups of four or five digits and next to a barcode. On a nano SIM the print is small and sometimes partial, so the carrier card is the more reliable place to read it. For a soldered SIM chip there is nothing to read by eye, and the number comes from the supplier’s delivery list or from the device.
On a phone
Phones show it in settings, usually in the About section or under SIM status, labeled ICCID. The layout differs between operating systems and versions. The code that shows the IMEI on most phones does not show the ICCID, although on phones with eSIM it often shows the EID as well.
On an IoT module
A cellular module reports its SIM’s ICCID through an AT command, and this is where it varies. Many modules answer to AT+CCID, others to AT+ICCID, and some use a command with a maker-specific prefix; the module’s AT command manual is the only reliable guide. The IMSI and IMEI are more consistent, because they have standard commands in 3GPP TS 27.007: AT+CIMI for the IMSI and AT+CGSN for the IMEI. The same standard also defines AT+CRSM, restricted SIM access, which can read the ICCID file directly on almost any module, at the cost of decoding the swapped digits yourself.
The module needs the SIM inserted and initialized before any of these will answer, so firmware usually reads the identifiers once the SIM reports ready, then logs or reports them.
Why IoT fleets track ICCIDs
On one phone the ICCID hardly matters. Across a few thousand devices it becomes the key that ties everything together.
Activation and lifecycle. SIMs for devices usually arrive in batches with a list of ICCIDs. Each card is activated, suspended or retired by its ICCID through the operator’s connectivity management platform, which also tracks states such as test, inventory, active and suspended. A device that ships with its SIM still inactive will sit silently until someone activates that ICCID.
Matching a SIM to a device. Recording each device’s ICCID and IMEI together at manufacture or first boot gives a pairing that later answers practical questions: which device is this SIM in, has a SIM been moved to different hardware, which card needs suspending when a unit is stolen. Many platforms can lock a SIM to one IMEI so it stops working if taken out and put in something else.
Usage and support. Data usage, network attach history and alerts are reported per SIM. When a device goes quiet, the ICCID is what support looks up to see whether the card is active, when it last attached and on which network. Invoices from operators are usually itemized per ICCID as well.
A stable key. Some IoT SIMs carry several IMSIs and switch between them to use different networks, so the IMSI is not a dependable key. The ICCID stays the same through those switches, which is why fleets key their records on it. The IoT SIM cards guide covers multi-network SIMs and management platforms in more detail, and the NB-IoT and LTE-M comparison covers the networks these SIMs attach to.
eSIM: EID versus ICCID
An eSIM is an eUICC, a SIM chip that can hold several operator profiles and have new ones downloaded remotely. That splits the job the ICCID used to do alone.
The EID, a 32-digit number, identifies the eUICC chip. It is fixed for the life of the chip, like the ICCID on a plastic card. Each profile on the chip has its own ICCID and its own IMSI, exactly as if it were a separate SIM card. Download a profile from another operator and the device gains a second ICCID; delete a profile and its ICCID is retired. Normally one profile is enabled at a time.
For a fleet that means tracking both numbers. The EID says which piece of hardware you are dealing with and is what a remote provisioning server needs to prepare a profile for it. The ICCID says which profile, and so which operator relationship, is in use at the moment. A device record that holds the IMEI, the EID and the currently enabled ICCID can answer almost any support question. An iSIM, where the SIM function runs inside the module’s chipset, uses the same model of one chip identity and one ICCID per profile.
The practical rule for device firmware is to read the ICCID, IMSI and IMEI at first boot and again whenever the SIM or profile changes, and report them with the device’s other status data. Where the protocol allows, a field in the device’s regular status message is enough; the IoT protocols explainer covers the options for carrying it.
Written by the IoT Crest editorial team. Facts in this article follow the editorial policy: only well-established behavior is stated and no figures are invented.