WiFi signal is measured in dBm, which stands for decibels relative to milliwatts (mW).
Absolute power of a signal is measured in wattage
dB scale does not define where you are starting from or what your ‘zero’ is. Therefore, we specify dBm, indicating that our scale is relative to 1 milliWatt of power. 0 dBm = 1 mW.
The reason you see negative values is that you are representing small but positive numbers, on a logarithmic scale. In logarithms, the value indicated represents an exponent… for example, under a log 10 scale, a value of -2 represents 10 to the -2 power, which equals 0.01.
Likewise, a negative dBm means that you are applying a negative exponent in your power calculations; 0 dBm equals 1 mW of power, so -10 dBm equates to 0.1 mW, -20 dBm equates to 0.01 mW, and so forth.
It is a lot easier, and more useful in some calculations, to describe a weak signal as -100 dBm as opposed to 0.0000000001 mW.
So remember – -1 dBm is significantly better than -100 dBm.
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