Invariably, every discussion about an RFID solution comes down to the same question:  How far will I be able to read the tag?  And, of course, everyone expects a quick and reliable answer.  For those of us that deal with RFID every day, we know that this seemingly innocuous question is anything but. 
RFID waves with RFID tags
For passive RFID (where the tag does NOT have its own power source), there are many variables that affect the read distance including:
    • the frequency of the RFID hardware 
    • type of antenna 
    • placement of antenna 
    • type of tag 
    • placement of tag 
    • item being tagged 
    • what the item is made of 
    • what the items contains 
    • the packaging around the item 
    • presence of metal 
    • presence of liquids 
    • temperature 
    • humidity 
    • other RF interference 

You get the picture.  It is easy to now see why there is no exact answer to this question without testing in your envirornment.  In following posts, I will discuss some of these points in additional detail.