dBm and watts

dBm = (10Log₁₀(milliWatts))

1 mW = 0 dBm

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Watts = 10^{((dBm - 30)/10)}

milliWatts = 10^(dBm/10)

Example:
Gps Received Signal Power in watts = 1.41e^-16W
Gps Received Signal Power in milliwatts = 1.41e^-13mW
Gps Received Signal Power in dBm = -128.5dBm

watts-dbm Calculator