Don't be confused by the terminology used when measuring fields. If we disregard the different national standards and the non-uniform usage of measurement units, we can classify field strength measurements into two categories: High frequency and Low frequency.

Along with the tables for converting quantities in electromagnetic fields, the following definitions are a useful aid during international discussions regarding safety in electromagnetic fields and environmental electromagnetic compatibility (EEMC).

In the low-frequency range up to about 30 kHz, the electric and magnetic fields must always be measured separately. The electric field strength is measured in V/m or kV/m (Volts per meter, kilovolts per meter). The magnetic field can be described using the magnetic induction (magnetic flux density) in units of T or mT (Tesla, millitesla) or in units of G or mG (Gauss or milligauss), or using the magnetic field strength in A/m (Amperes per meter).

In the high-frequency range, i.e. alternating fields in the MHz or GHz range (1 million or 1 billion oscillations per second), there is a lower range and an upper range. In the lower range up to about 30 MHz, the electric and magnetic field strengths are measured separately in V/m and A/m.

Above that, it is common to use the power flux density (Poynting's vector) in mW/cm² or W/m², even though only the electric or magnetic field component is measured. Here, the same conversion is used as is given in the tables.