# How can you determine electron cloud size?

Well, I guess you look at the orbital radial density distribution and see when it is zero at $r > 0$. This is not trivial...
If you just mean relative orbital sizes, higher principal quantum number $n$ usually indicates the orbital is larger:
You can see that orbitals with the ${l}_{\max}$ allowed at each $n$ increase in size with increasing quantum level $n$, since they taper off to zero at larger $r$.