According to Bohr's postulate, the angular momentum of an electron in the $n$-th allowed orbit of a hydrogen-like atom is:

Bohr postulated that only those orbits are allowed for which the angular momentum is an integer multiple of $\hbar = h/2\pi$, i.e. $mvr = n\dfrac{h}{2\pi}$, with $n = 1, 2, 3, \dots$. This quantisation condition, together with classical centripetal balance, gives the radii and energies of the Bohr orbits.