RFID reading distance depends on several factors including:
* Size of the tag’s antenna
* Tag chip
* Tags orientation in the reader field
* Strength of the reader field
* Environmental factors like metal, water or other material around the tag
* LF, HF and UHF near-field tags typically have a reading distance of ~1 ft (30 cm).
* UHF far-field tags typically have a reading distance of several m/ft but are strongly dependent on the environment.
* NFC Tags (HF) are designed for near-field communication with a smartphone or similar device and typically have a reading distance of ~1 in (2 cm).
More info view http://www.oppiot.com