dBm converter
Convert dBm to watts and back. Zero dBm is one milliwatt, and every 10 dB is another factor of ten.
That's about the same as a Wi-Fi router. That is about 100 milliwatts.
What it means
How strong is that signal?
Voltage figures assume the 50 ohm system impedance of radio equipment. In a 75 ohm cable television system the same power gives a different voltage.
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Three things worth knowing
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0 dBm = 1 mW, +30 dBm = 1 W
Every 10 dB multiplies by ten and every 3 dB roughly doubles, so +23 dBm is about 200 mW, which is a typical phone transmitting.
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Why an absolute decibel
Ratios alone cannot say how strong a signal is. Fixing the reference at one milliwatt turned the decibel into a unit of power you can add gains and losses to directly.
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dBm does not add to dBm
Adding two +10 dBm signals gives +13 dBm, not +20. You add dB to dBm; adding dBm to dBm multiplies watts by watts, which is meaningless.
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Background
About dBm
dBm is an absolute power, not a ratio: 0 dBm is exactly one milliwatt. That fixed reference is what lets radio engineers add a transmitter power in dBm to an antenna gain in dB and read the answer straight off.
A Wi-Fi router puts out about +20 dBm. Your phone hears it at −50 dBm when close, and the noise floor sits near −100.