It wouldn’t be possible to answer your question precisely since there are many variables that cannot be accounted for. Are the tags on densely or loosely packed items, for example? It makes a difference. How fast are the tagged items moving? And are the tags on RF-friendly material or on items containing water or metal, which can impact read rates? In general, I would say that you can read about 50 passive UHF RFID tags per second under favorable conditions—that is, on RF-friendly items, with minimal water or metal interference, and using high-quality tags and readers.
—Mark Roberti, Founder and Editor, RFID Journal
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