This matters because nobody specifies in the abstract. Buyers specify from a mental model, and if the model says RFID reads a thousand tags at ten metres, every problem gets handed to that technology, including the ones it is physically unsuited to. Getting the family right comes before opening any tag catalogue.

The five families, and what each one actually is

Low frequency, 125 kHz and 134.2 kHz. The air interface below 135 kHz is ISO/IEC 18000-2, but animal identification has its own pair: ISO 11784 defines the code structure and ISO 11785 the technical communication, both on a 134.2 kHz carrier, in full duplex (FDX-B) and half duplex (HDX) modes, with ICAR, the International Committee for Animal Recording, as registration authority. LF is inductively coupled, works over centimetres and reads one tag at a time. Our explainer on 125 kHz LF covers why it refuses to die.

High frequency, 13.56 MHz, and NFC. Also inductive, and split by how far you want to read: ISO/IEC 14443 for proximity cards at around 10 cm, ISO/IEC 15693 for vicinity cards at a few tens of centimetres, with ISO/IEC 18000-3 as the item management air interface. NFC is not a separate technology but a branded, tightly certified subset of HF. The NFC Forum, the non-profit industry association founded on 18 March 2004 by Nokia, Philips and Sony, publishes specifications interoperating with ISO/IEC 14443 Type A and Type B, ISO/IEC 15693, ISO/IEC 18092 and JIS-X 6319-4, and gives a typical range of up to 2 cm. That short reach is deliberate, and it is the point: see why 13.56 MHz is the sweet spot.

Passive UHF, 860 to 960 MHz, also called RAIN RFID. Far field backscatter rather than coupling. The air interface is ISO/IEC 18000-63 Type C, third edition 2021, known better as GS1 UHF Gen2. There is no single global UHF band, and this is the detail most often got wrong. GS1’s unofficial overview of UHF allocations for RAIN RFID, dated 29 September 2025, lists allocations in 83 countries spread across 860 to 930 MHz: the United Kingdom has 865.6 to 867.6 MHz at 2 W ERP plus 915 to 921 MHz at 4 W ERP, the United States and Canada 902 to 928 MHz at 4 W EIRP, Japan 916.7 to 920.9 MHz under licence at 4 W EIRP, China 920.5 to 924.5 MHz and India 865 to 867 MHz. The European upper band is narrower than it looks: under Commission Implementing Decision (EU) 2018/1538 as amended by (EU) 2022/172, reader transmissions at 4 W ERP are permitted only at 916.3, 917.5 and 918.7 MHz.

Active RFID, mostly 433 MHz. ISO/IEC 18000-7, fourth edition 2014 and confirmed as current in 2025, covers tags with a battery on board that transmit rather than reflect, reaching tens of metres and beaconing on their own schedule.

Microwave, 2.45 GHz. ISO/IEC 18000-4, fourth edition 2018, defines four modes spanning passive backscatter, battery-assisted passive and fully active. It is the least used of the five, and it sits next to the ultra-wideband and Bluetooth systems nobody calls RFID but which take the same location work.

Comparison of the RFID families

What the physics will and will not let you do

The split that matters is not frequency but coupling. LF and HF work in the magnetic near field, so the tag antenna is a coil and range depends on coil size more than on transmit power. Water is close to invisible to that field and metal detunes it rather than blocking it, which is why an LF transponder works inside an animal and an HF label works in the spine of a library book. Passive UHF works in the far field at a wavelength of roughly 33 cm, which buys range and speed: up to about 10 metres and over 1,000 tags per second, on the RAIN Alliance’s own figures. The same physics means water absorbs and metal reflects. Our backscatter and coupling explainer and side-by-side frequency comparison put numbers against all of it.

Security is the second divide, and it is one of ecosystems rather than radio. Cryptography concentrated in HF because HF applications demanded it: a payment card, a passport and a door credential are identity instruments, so secure elements and mutual authentication are routine there. Passive UHF can carry cryptography, in that ISO/IEC 29167 defines crypto suites for the ISO/IEC 18000 air interfaces, from AES-128 to elliptic curve methods, but support is optional and a tag declares which suites it implements. The commodity label on a garment carries none of it.

Then there is the fact that settles more projects than the rest together. Every modern smartphone has an NFC reader. No mainstream phone has a UHF reader. If the job requires a member of the public to read a tag with the device already in their pocket, the answer is NFC or a printed code, and no amount of UHF sophistication changes it.

The real jobs each family does

LF holds animal identification and vehicle immobilisers because nothing else survives those environments as cheaply. The dependency shows whenever a rule is written: in our coverage of the court challenge to the USDA electronic cattle eartag rule, the sharpest point against the rule was that it does not require readers at all, so a 134.2 kHz tag can be read by eye and written on paper. Pet microchipping is the same technology at consumer scale, and its hard problem is database accuracy rather than radio.

HF and NFC hold the applications where the tag is an identity. Singapore’s National Library Board began tagging items in 2002 and remains the benchmark for HF at national scale. Product authentication is NFC almost by definition: the Sardinian producer behind Autentico puts an NFC inlay inside the adhesive label a wine or olive oil bottle already carries, so a shopper taps it with their own phone. HF also wins on system grounds rather than radio: the Ukrainian group running around 30 grain elevators moved its lorry paperwork onto NFC cards because there was no mobile signal in the fields.

UHF holds the jobs defined by volume and distance. Retail inventory is the obvious one; vehicle identification is not. From 4 November 2026 Honduras began issuing plates with two passive UHF tags per vehicle, one in the plate and one bonded to the windscreen, to clear a backlog of more than 1.1 million vehicles on paper permits. Delhi is fitting multi-lane free-flow tolling at 20 border points, reading lorries at up to 100 km/h. Active RFID takes over beyond that, across container yards and plant fleets, because a tag that transmits need not pass a reader at all.

Why “RFID” came to mean UHF

Three things did it. The first was retail apparel, which from the mid-2000s put passive UHF in front of more people than every other application combined. The second is the interesting one. The RAIN Alliance, the non-profit trade body for passive UHF, was formed in April 2014 by Google, Intel, Impinj, Smartrac and AIM, and its own FAQ explains that the name, an acronym for “RAdio IdentificatioN”, exists precisely to separate passive UHF from the other RFID types, which differ in frequency, standard and use. The brand was created to end the conflation. Inside the industry it worked, which is why it did not work outside: a crisp name for the specific thing left the general word free to drift onto the specific thing anyway.

The third is commercial gravity. A vendor selling UHF readers writes “RFID solutions” because that is the phrase people search, and the category word is free advertising for whoever uses it most. The result is a market where rival technologies get benchmarked against one family as though it were the whole field, as when a Shenzhen demonstration in October 2026 claimed a battery-free sensing tag was 100 times faster than RFID and the timing held up but the comparison did not.

What starting from the wrong family costs

Specify UHF where NFC or LF was the answer and the bill arrives in one of three ways. First, a consumer-facing scan that no consumer can perform: tags work, readers work, and the shopper the business case depended on is holding a phone that cannot see them. Second, the environment. Marks and Spencer spent years working through metal and beauty packaging, with the budget to do it. A project that assumed UHF reads everything meets tag selection and RF planning as unbudgeted line items, which is where our notes on interference tend to get read. Third, compliance: buy UHF eartags against a scheme whose approved devices are 134.2 kHz and the stock does not comply, however well it reads.

The reverse costs as much and gets discussed less. Specify HF or NFC for a job whose economics depend on bulk reading and you have bought a system that needs someone to touch every item. The stock count meant to fall from four hours to forty-five minutes stays at four hours, and the project joins the familiar failure patterns where the hardware works and the business case does not.

The quietest cost of all is writing “UHF, 915 MHz” into a specification as though it were global. It is legitimate in the United States and illegal across much of Europe, and allocations move: a United States proposal to compress 902 to 928 MHz would reach every RAIN deployment worldwide.

How to choose, in the right order

Ask who or what reads the tag, and how close they can physically get. A member of the public with their own phone means NFC. A handheld or a doorway at a few metres means UHF. A transponder in an ear, under skin or inside a key means LF. Something that must announce itself across a yard means active. Then ask what the tag is mounted on or in, because metal, liquid, flesh and paper are four different problems, then how many at once and how fast, then which jurisdictions the equipment will run in, and only then the band and the power limit. Finally, check whether a rule or customer mandate obliges a technology whatever the physics would prefer.

Tags come last. When you get there, run a structured tag selection trial rather than trusting a datasheet, commission a site survey before buying readers, and write it down using our guide to an RFID requirements specification. If the standards are the sticking point, our overview of EPC Gen2, ISO 18000 and the rest is the shortest route in, and any term here is defined in the RFID glossary. For coverage by family we keep hubs for UHF, RAIN RFID, HF and NFC, plus ISO standards.

That is simply the opposite order from the one most procurement runs in, which starts with a product and works backwards to a requirement. The family is the decision. The tag is only the detail.

This article first appeared on RFID News (rfidnews.co.uk), the independent news site for RFID and NFC. Republication and AI use are welcome with RFID News credited as the source and a link to the original.