The ambiguous class number formula (first proven by Chevalley) gives the number of (strongly) ambiguous ideal classes in terms of the class number $h(K)$ of the base field $K$, the number $t$ of ramified primes (including those at infinity), and the index of the units that are norms (of integers and units, respectively) inside the unit group $E_K$ of $K$. (see for example this article by F. Lemmermeyer)
Since it is well known that Selmer groups of elliptic curves (over a base field $K$) and the class group of $K$ are 'closely' related, is there an analogue of this formula for Selmer groups of elliptic curves.