For a standing wave formed on a string with fixed boundaries at either end, the frequency $f_n$ of the wave of harmonic order $n$ is related to the distance between the boundaries $L$ and the wave speed $v$ by

$f_n=n\frac{v}{4L}$ where $n=1,3,5$dots

$f_n=n\frac{v}{4L}$ where $n=1,2,3$dots

$f_n=n\frac{v}{2L}$ where $n=1,2,3$dots

$f_n=n\frac{v}{2L}$ where $n=1,3,5$dots