Cell tower signal strength

May 17, 2022 · Decibel-Milliwatts: The Most Accurate Cell Phone Signal Strength Measurement. Cell phone signals are radio waves (AM/FM) operating within certain cellular frequencies. Decibel-milliwatts, or dBm for short, measures the strength of the wave. These are expressed in negative numbers. Cellular signal strength ranges from -50 dBm (great signal or full bars) to -120 dBm (very poor signal or a dead zone)..