### Question

What exactly is a dBm and how would you measure it?

It is often convenient to express power or voltage ratios, (or any ratio for that matter), using a logarithmic scale. For example the definition of a power ratio in terms of decibels is:

Power ratio in dB = 10*Log(P2/P1)

for example if the output power of a device is found to be half of the input power then we could express this as -3dB (plug in some numbers to see this).

Now to answer your question concerning dBm. We use dBm to express absolute values of power relative to a milliwatt. The definition is

Measure of power in dBm = 10*Log(power in milliwatts / 1 milliwatt)

So if you wanted to express your power in terms of dBm instead of milliwatts you would use the above equation.

For example if your power level were 1 milliwatt, you could also call this power level 0 dBm. Or if your power level were 100 milliwatts you could instead say 20 dBm.

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### Science Quote

'Never regard study as a duty, but as the enviable opportunity to learn to know the liberating influence of beauty in the realm of the spirit for your own personal joy and to the profit of the community to which your later work belongs.'

Albert Einstein
(1879-1955)