Full width at half maximum
Full width at half maximum (FWHM) is an expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value.
The term full duration at half maximum (FDHM) is preferred when the independent variable is time.
The convention of "width" meaning "half maximum" is also widely used in signal processing to define bandwidth as "width of frequency range where less than half the signal's power is attenuated", i.e., the power is at least half the maximum. In signal processing terms, this is at most −3 dB of attenuation, called "half power point".
If the considered function is the normal distribution of the form
Any translating element was omitted, since it does not affect the FWHM. For this impulse we have:
where arsech is the inverse hyperbolic secant.
- This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
See also 
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