The answer really depends on the type of transponder and the numbering scheme that you choose. You could purchase low-frequency (LF), high-frequency (HF), ultrahigh-frequency (UHF) or some type of active transponders, and you could write whatever serial number into the transponder that you like.
GS1 and EPCglobal have created a standardized numbering scheme for UHF transponders, known as the Electronic Product Code (EPC). To find out the maximum number of digits that an EPC can be, I reached out to Sue Hutchinson, EPCglobal’s director of industry adoption. Here is her response:
“EPC is an encoding method for several different identifiers, or keys. Each one would have a different number of digits that are possible to express, in either 96 bits or 198 bits (the two most common lengths for EPCs). For the most common key, the serialized GTIN-96—or SGTIN-96—those 96 bits contain some simple reader instructions, followed by the GTIN (13 decimal digits without its bar-code check digit, which is unnecessary for RFID operations), followed by a serial number (which is roughly 12 decimal digits in length). Other keys are of other lengths. All of the different EPC encodings and their decimal or alphanumeric equivalents are fully described in the EPC Tag Data Standard, which can be downloaded by anyone at this site: http://www.gs1.org/gsmp/kc/epcglobal/tds.”
—Mark Roberti, Founder and Editor, RFID Journal
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