IMSI Decoder / Encoder
Decode or encode an IMSI (International Mobile Subscriber Identity) — extract MCC, MNC, country, operator name, and MSIN from any 15-digit subscriber identity.
MCC
3 digits
decimalMNC
2 or 3 digits
decimalMSIN
up to 10 digits
decimalMNC length
MNC length is not encoded in the IMSI — auto-detect uses the operator database.
IMSI Format Reference
An IMSI (International Mobile Subscriber Identity) is the unique identifier for every SIM card or eSIM on a mobile network. It is defined by ITU-T E.212 and stored on the SIM. Unlike a phone number, an IMSI never changes when the subscriber keeps the same SIM.
IMSI structure
IMSI = MCC (3) + MNC (2–3) + MSIN (≤10) ≤ 15 digits total
All fields are decimal — there is no hexadecimal encoding in an IMSI.
| Field | Length | Format | Description |
|---|---|---|---|
| MCC | 3 digits | decimal | Mobile Country Code — identifies the country |
| MNC | 2–3 digits | decimal | Mobile Network Code — identifies the operator |
| MSIN | up to 10 digits | decimal | Mobile Subscriber Identification Number — unique within the PLMN |
Example — Airtel India subscriber
IMSI : 404100123456789
MCC : 404 (India 🇮🇳)
MNC : 10 (Airtel IN)
MSIN : 0123456789
The MCC and MNC together form the PLMN — the same PLMN used in CGI / ECGI / NCGI cell identifiers. An IMSI identifies the subscriber; a CGI identifies the cell they are camped on.
Frequently Asked Questions
What is an IMSI?▾
IMSI (International Mobile Subscriber Identity) is a unique number stored on every SIM card that identifies the subscriber on a mobile network globally. It is used internally by the network for authentication, routing, and tracking — it is never shown to the end user. The IMSI consists of a 3-digit MCC, a 2 or 3-digit MNC, and up to 10 digits of MSIN, with a maximum total of 15 digits as defined by ITU-T E.212.
What is the difference between IMSI and MSISDN?▾
IMSI identifies the SIM card (subscriber identity), while MSISDN is the phone number (the dialable number in E.164 format). A single SIM has one IMSI but can have multiple MSISDNs (e.g. voice and data numbers). The IMSI is used for authentication and roaming signalling; the MSISDN is used for call routing. Telecom engineers see both in CDRs, HLR/HSS records, and network logs.
How do I know if an MNC is 2 or 3 digits?▾
The IMSI string itself does not encode the MNC length — it must be determined from the PLMN specification or operator database. Most operators in Europe, Asia, and Africa use 2-digit MNCs. The United States and Canada commonly use 3-digit MNCs. This decoder uses the built-in operator database to auto-detect the correct length. If your operator is not in the database, use the MNC length selector to force 2-digit or 3-digit.
Where does the IMSI appear in telecom logs?▾
The IMSI appears in many places: SIM card records (ICCID files), HLR/HSS subscriber data, CDRs (Call Detail Records), Diameter signalling (S6a interface, ULR/ULA messages), MAP (Mobile Application Part) protocol messages, and network management exports. In LTE/5G logs it also appears in NAS (Non-Access Stratum) Attach Request and Registration Request messages.
Is an IMSI a security risk to expose?▾
Yes. An IMSI identifies a specific SIM card and, in combination with the MSIN, can enable IMSI-catching attacks (using fake base stations to intercept calls or track location). Modern 4G/5G networks use SUPI (Subscription Permanent Identifier) and transmit a protected SUCI (Subscription Concealed Identifier) over the air instead of the raw IMSI. Engineers handling IMSIs in logs should treat them as personal identifiable information (PII).