dBm to mW Converter
Radio, Wi-Fi and network gear often lists power in dBm, a logarithmic scale. Enter the figure to see the same power in milliwatts, a plain amount you can compare.
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How it works
Power in milliwatts is 10 raised to the power of the dBm figure divided by 10. So 0 dBm is 1 mW, 10 dBm is 10 mW, and 20 dBm is 100 mW.
Because the scale is logarithmic, adding 3 dBm roughly doubles the power and subtracting 3 dBm roughly halves it. Negative dBm values give small fractions of a milliwatt.
Worked example
A level of 20 dBm works out to 100 milliwatts, the same power written on a straight scale.
Questions
What is dBm?
dBm is decibels relative to one milliwatt. It is a logarithmic scale, so a change of 10 dBm always means ten times the power, at any level.
Why is the answer so small for negative numbers?
A negative dBm figure means less than one milliwatt. Every 10 dB down divides the power by ten, so -30 dBm is 0.001 mW.
Can I convert milliwatts back to dBm?
Yes, with a formula. Take 10 times the base-10 logarithm of the milliwatt figure. This page only converts in the direction shown.
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