If you have ever researched mobile signal boosters or consulted a telecom engineer, you have likely encountered terms like -85 dBm or 65 dB gain. For non-engineers, seeing negative numbers can be confusing. Why is a signal measured in negatives, and why is -70 dBm actually much stronger than -100 dBm?
What Does dBm Actually Measure?
dBm stands for decibel-milliwatts. It is an expression of absolute power relative to one milliwatt (1 mW = 0.001 watt). Because radio waves emitted by cell towers lose immense amounts of energy traveling through miles of open air and building walls, the power that reaches your phone is tiny—often less than a billionth of a watt.
Instead of writing numbers with a dozen decimal zeros (like 0.0000000001 watts), engineers use a logarithmic scale based on decibels. On this scale, 0 dBm equals exactly 1 mW. Any power level less than 1 milliwatt is represented as a negative number.
The Golden Rule of the Logarithmic Scale
Because the decibel scale is logarithmic rather than linear:
- Every +3 dB increase doubles the signal power.
- A +10 dB increase represents a 10-fold increase in signal power.
- A +20 dB increase represents a 100-fold increase in signal power!
This means that a signal of -80 dBm is not just slightly better than -100 dBm—it is literally 100 times more powerful! That is why even a moderate booster delivering +65 dB of gain can transform an unusable room into a full-speed connectivity zone.
Learn more about how our equipment amplifies these numbers on our Triple Band Booster page or get your premises audited.