  We generalize the time-honored Weinberg's compositeness relations by
including the range corrections through considering a general form factor. In
Weinberg's derivation, he considered the effective range expansion up to
$\mathcal{O}(p^2)$ and made two additional approximations: neglecting the
non-pole term in the Low equation; approximating the form factor by a constant.
We lift the second approximation, and work out an analytic expression for the
form factor. For a positive effective range, the form factor is of a
single-pole form. An integral representation of the compositeness is obtained
and is expected to have a smaller uncertainty than that derived from Weinberg's
relations. We also establish an exact relation between the wave function of a
bound state and the phase of the scattering amplitude neglecting the non-pole
term. The deuteron is analyzed as an example, and the formalism can be applied
to other cases where range corrections are important.
