Distance can be calculated by using this formula
TxPower (dBm) - For EYE Beacons/Sensors it can be found on EYE App configurator
RSSI - Can be also checked on EYE App or by parsing data that has been sent from beacon to the server (This can be found on our WIKI page).
n - constant depends on the Environmental factor. Range 2-4, usually n = 2
Hope this information helps you,