# -3dB on filters, just approximated?

I have been told that -3dB is when you get half the power or equivalently the original voltage divided by the square root of 2.

Nonetheless, doing the calculations I get 3.01029dB.

I figure this is because the 3dB value is just the aproximated value of what I have gotten but maybe I am mistaken somewhere, so is the 3dB just an approximation or am I mistaken?

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20log$_{10}(\dfrac{1}{\sqrt2})$ = 3.01029995664 !