When I first started researching electromagnetic fields  one of the biggest problems I had was getting my head around all the jargon; trying to understand what all the different measurement units that are used to quantify EMFs meant.
Most people have vaguely heard of terms like Volts, Watts, Gauss and Hertz but then between having heard of a term and having even a vague understanding of its meaning, there is often a big gulf. Here I hope to answer at least some of your questions.
EMFs are mainly characterized in terms of frequency and strength.
Frequency is measured in hertz, which means cycles per second. Your electricity supply for instance, operates in the 50 or 60 Hz frequency range, depending on where you live. FM radio operates in the mega hertz range, so when it says 98.6 on the dial that means 98.6 MHz (or 98,600,000 hertz). Cell phones and similar wireless devices operate mainly in the 1-2 GHz range (1GHz = 1000,000,000 Hz).
The other parameter is signal strength. So at any given frequency, 50Hz or 98.6 MHz or 1.8 GHz (that used by many cell phone operators), you can have different signal strengths. And these different signal strengths are measured in different units, Gauss, Volts, Watts etc. according to the frequency and according to the nature of the signal.
What Are The Most Common Units of Measurement For Measuring RF Radiation?
RF radiation  or radio frequency radiation is situated in the GHz frequency range.
The most common units of measurement for measuring radio frequency radiation are microWatts per square meter (µW/m2), microWatts per square centimeter (µW/cm2), milliWatts per square meter (mWm²) and Volts per meter (V/m). And herein lies the problem, there is no accepted standard on this.
Firstly lets get clear on how to convert between microWatts per square meter (µW/m2), microWatts per square centimeter (µW/cm2) and watts per square meter (W/m²).
To convert between units expressed in square meters is quite simple (remember that “mW” means “milliWatts” and “µW” means microWatts):
1 W/m² = 1000 mW/m² = 1000,000 µW/m²
Similarly in square centimeters:
1W/cm² = 1000 mW/cm² = 1000,000 µW/cm²
Where this gets more complicated is converting between units that are expressed in square meters and those that are expressed in square centimeters for instance:
1 μW/cm² = 10,000 μW/m²=10mW/m²
What Are The Best Units of Measurement For Measuring RF Radiation?
That depends on what your objectives are. But for personal EMF measurement we are interested in relatively low levels of radiation because we now know that even relatively weak RF signals have biological consequences. Most RF meters for personal use have now incorporated this parameter. For instance the Cornet meters  now use V/m and mW/m² and the Acoustimeter  uses V/m and μW/m². I recommend meters that give readings in V/m this is the most meaningful measurement for personal testing and protection.
What is the Advantage of Obtaining Measurements in V/m?
Technically speaking W/m² (and its derivatives mWm², μW/cm² etc.) measures something called Power Flux Density. PFD is measured by averaging the power over time (6 minutes for official RF measurements) and is therefore most relevant to measuring the heating effect of RF radiation.
Studies show that it is the pulsing effects of EMFs that are particularly dangerous. V/m is considered the best unit of measurement for measuring microwave signals at non-thermal levels (as used by WiFI and cell phones and the like) because it gives peak signal strength (some devices have peak power levels up to 100 times more than their average power levels).
Conversion Formulas for Radio Frequency (RF) Radiation
The most commonly asked question is how to convert between W/m² and V/m. There is a conversion formula for this but W/m²only converts into V/m for continuous signals (things like VHF and FM radio signals).
Formula for Conversion from W/m² to V/m
V/m = (W/m2 x 377)1/2
Example: to convert 10 W/m2 into V/m you would make the following calculation, (10W/m2 x 377)1/2 = 61 V/m
Formula for Conversion from V/m to W/m²
W/m² = (V/m)² / 377
Example: to convert 6 V/m into W/m² you would make the following calculation, (6 x6)/377 = 0.1 W/m2
But W/m² is rarely used for personal RF exposure because the levels which impact health are known to be of lesser strength by several magnitudes
Measurement Units for AC Magnetic Fields
The most common units of measurement for AC magnetic fields are Gauss and Tesla.
In Canada and the US the standard measurement unit is Gauss and in most other parts of the world it is Tesla. Both units measure exactly the same thing, the magnetic field generated by current flow. Because we know that even relatively weak magnetic fields have biological consequences the most common units of measurement are milliGauss (mG) and microTesla (μT), these are the measurement units used by the Cornet ED75 and Trifield 100XE (mG only).
See the formula below for a better understanding of their relationship.
Formula for Conversion between Gauss and Telsa
The conversion is quite simple:
1mG = 0.1 μT
which also means:
1 μT = 10 mG
Measurement Units for AC Electric Fields
AC electric fields are commonly measured in Volts/meter. So this is the same unit of measure as RF radiation, as explained above, the difference is the frequency. With RF radiation we are mainly concerned with radiation in the GHz range whereas AC electric fields are typically in the 50/60 Hz, thats to say the frequencies found in electrical wiring and powerlines. The Trifield TF2  measures AC electric fields in V/m.
I hope this gives you a basic understanding of what the different measurement units that are used to measure EMFs mean.