Crest Factor ‘or’ Peak Factor is defined as the ratio of the maximum value to the R.M.S value of an alternating quantity.
C.F. ‘or’ P.F. = \(\frac{{Maximum\;Value}}{{R.M.S\;Value}}\)
The form factor is defined as the ratio of the RMS value to the average value of an alternating quantity.
F.F. (Form factor) = \(\frac{{R.M.S\;Value}}{{Average\;Value}}\)
For a sinusoidal waveform:
Form Factor = 1.11
Crest Factor or Peak factor = 1.414
WAVEFORM 
SHAPE

MAX. VALUE 
AVERAGE VALUE 
RMS VALUE 
FORM FACTOR 
CREST FACTOR 
SINUSOIDAL WAVE 
\({A_m}\) 
\(\frac{{2{A_m}}}{\pi }\) 
\(\frac{{{A_m}}}{{\sqrt 2 }}\) 
\(\frac{{\frac{{{A_m}}}{{\sqrt 2 }}}}{{\frac{{2{A_m}}}{\pi }}} = 1.11\) 
\(\frac{{{A_m}}}{{\frac{{{A_m}}}{{\sqrt 2 }}}} = \sqrt 2 \) 

SQUARE WAVE 
\({A_m}\) 
\({A_m}\)

\({A_m}\)

\(\frac{{{A_m}}}{{{A_m}}} = 1\) 
\(\frac{{{A_m}}}{{{A_m}}} = 1\) 

TRIANGULAR WAVE 
\({A_m}\) 
\(\frac{{{A_m}}}{2}\) 
\(\frac{{{A_m}}}{{\sqrt 3 }}\) 
\(\frac{{\frac{{{A_m}}}{{\sqrt 3 }}}}{{\frac{{{A_m}}}{2}}} = \frac{2}{{\sqrt 3 }}\) 
\(\frac{{{A_m}}}{{\frac{{{A_m}}}{{\sqrt 3 }}}} = \sqrt 3 \) 

HALFWAVE RECTIFIED WAVE

\({A_m}\) 
\(\frac{{{A_m}}}{\pi }\) 
\(\frac{{{A_m}}}{2}\) 
\(\frac{{\frac{{{A_m}}}{2}}}{{\frac{{{A_m}}}{\pi }}} = \frac{\pi }{2}\) 
\(2\) 