The embodiments herein measure the tag to noise ratio (TNR) for a tag on an item (e.g., a package) to determine a location of the item in a warehouse. In one embodiment, the TNR is derived by comparing a measured performance parameter for a tag of interest to the combined measured performance parameters for other tags measured by the same reader or for the same tag when measured by a different RFID reader. The higher the TNR, the greater likelihood the tag is within an area assigned to the reader. In another embodiment, the TNR is derived from comparing the signal strength of a tag as measured by multiple RFID readers. In another example, respective TNR values for a plurality of tags detected by a reader can be compared to determine which tag is being carried by an associate.