dBm to mW Converter & Free Space Path Loss (FSPL) Calculator

The decibel-milliwatt (dBm) unit provides an expression of absolute radio frequency and optical power referenced to one milliwatt (1 mW = 0 dBm). In telecommunications and wireless engineering (Wi-Fi, cellular, microwave links, and optical transport), power levels span enormous dynamic ranges—from tens of Watts down to fractions of a picowatt. Expressing these extremes in linear milliwatts or Watts would necessitate cumbersome decimal scientific notation. Converting to a logarithmic decibel scale reduces complex cascading gain and attenuation stages to elementary additions and subtractions. A foundational mental model for RF engineers is the 'Rule of 3s and 10s': an increase of +3 dB doubles linear power in milliwatts (e.g. 10 dBm = 10 mW, so 13 dBm = 20 mW), while a decrease of -3 dB halves power. An increase of +10 dB multiplies linear power by a factor of 10 (20 dBm = 100 mW, 30 dBm = 1,000 mW = 1 Watt), and a +20 dB increase represents a 100-fold power multiplication. Beyond direct power conversions, this calculator implements Free Space Path Loss (FSPL) modeling governed by ITU-R P.525. FSPL quantifies the geometric spreading loss of an electromagnetic wavefront propagating through unobstructed free space. Governed by the inverse-square law, received signal density attenuates proportionally with distance squared and carrier frequency squared, serving as the benchmark foundation for wireless point-to-point link planning.