Electricity consists of electric and magnetic fields. The electric fields are measured in volts per meter (V/m) and the magnetic fields are measured in milliguass (mG).
Radio frequency radiation also consists of electric and magnetic fields, however other than in the near field exposure (typically a few inches or feet at most) the fields are coupled together. A formula for power density has been adopted for this far field exposure. Green Evolution generally uses the power density measurement of microwatts per centimeter squared (uW/cm2).
Please read PowerWatchUKs page on conversions of measurements for more on this -
To convert W/m2 to mW/cm2 divide by 10.
Here are links for converting the various readings on RF emissions -http://www.radioing.com/eengineer/rfcalc.html
And two sites for calculating levels without taking readings -