Pet Microchip ISO Standards Explained: 15-Digit Chips and International Compatibility

If you have spent any time preparing your pet’s travel documents, you will have noticed that almost every country requires an ISO microchip. But what does that mean, and why do some pets fail to meet the standard even though they are already chipped?

What Is an ISO Microchip?

An ISO microchip is a radio-frequency identification (RFID) chip that conforms to the international standards ISO 11784 and ISO 11785. These standards define:

ISO 11784: The data structure of the chip – specifically, that the identification code is 15 digits long and follows a defined format
ISO 11785: The technical requirements for reading the chip – frequency (134.2 kHz), communication protocol and how readers interact with the chip

When a government or veterinarian says “ISO microchip,” they mean a chip that stores a 15-digit number and operates at 134.2 kHz.

Why 15 Digits Matters

Older microchips – particularly those implanted in the USA and some other countries before approximately 2007 – were typically 9 or 10 digits, not 15, and operated at 125 kHz rather than 134.2 kHz. These are often referred to as AVID or FDXB chips.

The problem is that standard ISO readers cannot read 125 kHz chips. At international border posts, the standard scanner used will only pick up ISO 15-digit chips. If your pet has an older non-ISO chip:

A scanner at a European, Australian, UK, Japanese or other international border post may not detect it
The pet may be treated as unidentified, even though the chip is physically present
This can lead to significant delays, quarantine or refusal of entry

How to Check Your Pet’s Chip

Ask your vet to scan your pet with an ISO-compatible reader. Most modern multi-frequency readers can detect both ISO and legacy chips, but confirm this. The scan should display a 15-digit number starting with a country code (for UK-chipped dogs, the number starts with 999; for USA-chipped dogs, it typically starts with 985 or 0; for EU-chipped pets, a country-specific prefix is used).

If your pet has a non-ISO chip, the options are:

Implant a second ISO chip: Most vets can implant a second 15-digit ISO chip alongside the existing one. Both are then documented in the pet’s records. Note: most international travel authorities require the ISO chip number to be the one on all health certificates and vaccination records
Accept the non-ISO chip and use a universal scanner: In some jurisdictions (notably for USA domestic travel), older chips are still acceptable; confirm with your specific destination’s requirements

Linking the Chip to the Vaccination Record

A critical point that causes many document failures: the ISO chip number must be on all vaccination records before the vaccination is given, not after. If your pet was vaccinated and then chipped (or if the chip number was recorded incorrectly on the vaccine certificate), the vaccination record is considered invalid for international travel purposes.

This is especially relevant for the rabies titre test: the titre test result is only recognised if the chip number matches the number on the vaccination record that preceded the test.

Chip Registration

In many countries, microchip registration on a national or international database is strongly recommended or required. In the UK, microchip registration is mandatory for dogs under the Microchipping of Dogs (England) Regulations 2015. Key registries include:

PETtrac / Agria (UK)
Petlog (UK)
ANIS (Ireland)
European Pet Network (EU)
Found Animals (USA)
PetMaxx / HomeAgain (USA)

Ensure your contact details are current on the registry used in your home country, and consider registering on an international database such as Europetnet or the AVID International registry if you are moving abroad.

Sources: ISO 11784:1996; ISO 11785:1996; FEDIAF microchip guidance; UK Microchipping of Dogs (England) Regulations 2015; USDA APHIS microchip guidance for international travel.