When I go through Electroencephalography,

Band    Frequency (Hz)
Delta   < 4
Theta   ≥ 4 and < 8
Alpha   ≥ 8 and < 14
Beta    ≥ 14 

How much are wave length of brain wave?

Thanks for Bryan Krause's comment,"Brain waves" aren't EM waves,but mechanical wave has width as we known.

And it's obvious brain wave is some kinds of wave, with frequency and scale.

When someone is awake, with his eyes closed, the EEG is dominated by the α (alpha) band. This type of waves is characterized by a frequency of 8-13 Hz and a normal width <50 microvolts (µV).

If the subject opens his eyes, α waves disappear and another wave type becomes evident: the β (beta) type. These brainwaves have a higher frequency (30-35 Hz) and a width of 25-30 µV.

Then I still want to know Does brain wave has wave length?.

representations of different brain wave bands

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    $\begingroup$ Does this answer your question? Are brain waves electromagnetic waves? $\endgroup$ – Bryan Krause Feb 17 at 3:52
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    $\begingroup$ "Brain waves" aren't EM waves, see attached duplicate. The frequencies are in Hz which is units of 1/s. So you could say the length (as in duration) of a 4 Hz brain wave is .25 seconds, but that's just another way of describing the frequency. There is no length in space like an EM wave. $\endgroup$ – Bryan Krause Feb 17 at 3:55
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    $\begingroup$ @BryanKrause,aren't EM waves.Can we say brain waves are waves with wave width? $\endgroup$ – kittygirl Feb 17 at 7:26
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    $\begingroup$ @kittygirl There is no length (or width or anything else) in space, as I wrote in a comment above. The axes are voltage and time. The "waviness" at different frequency is because the signals in those plots are filtered to include only certain frequencies, so the "width" of a wave takes more or less time. Brain waves are not EM waves. $\endgroup$ – Bryan Krause Feb 17 at 21:01
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    $\begingroup$ @ChrisRogers From Wikipedia: "wavelength is inversely proportional to frequency". So WL = 1/f, or in units, m or s = 1/Hz. $\endgroup$ – Arnon Weinberg Feb 22 at 18:41

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