Unit conversions
Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt. To express an arbitrary power P as x dBm, or go in the other direction, the following equations may be used:
x = 10 \log_{10}(1000P)\, or, x = 10 \log_{10}P + 30\,
and
P = 10^{(x/10)}/1000 \,
where P is the power in W and x is the power ratio in dBm. Below is a table summarizing useful cases:
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