  We propose a entanglement measure for pure $M \otimes N$ bipartite quantum
states. We obtain the measure by generalizing the equivalent measure for a $2
\otimes 2$ system, via a $2 \otimes 3$ system, to the general bipartite case.
The measure emphasizes the role Bell states have, both for forming the measure,
and for experimentally measuring the entanglement. The form of the measure is
similar to generalized concurrence. In the case of $2 \otimes 3$ systems, we
prove that our measure, that is directly measurable, equals the concurrence. It
is also shown that in order to measure the entanglement, it is sufficient to
measure the projections of the state onto a maximum of $M(M-1)N(N-1)/2$ Bell
states.
