dB(uV/m) is decibel above a microvolt per meter reference

Radiated Measurement Units:

FS = Field strenght
RSSI = Voltage at the antenna connector
dB(uV/m) = decibel ratio referenced to a microvolt per meter = Field Strength
Ke = Antenna Factor = losses associated with the receive antenna

Field strength calculated as follows:

Calculate from and to other units ?
Use the 'On-line RF calculator'.