# Pion decay constant

${\displaystyle f_{\pi ^{\pm }}=130.41\pm 0.03\pm 0.20~{\mbox{MeV}}}$
${\displaystyle f_{\pi ^{0}}=130\pm 5~{\mbox{MeV}}}$
Beware: There are several conventions which differ by factors of ${\displaystyle \scriptstyle {\sqrt {2}}}$. The textbook by Weinberg uses the value 184 MeV. The textbook by Peskin and Schroeder uses the value 93 MeV.