  Entanglement and steering are used to describe quantum inseparabilities.
Steerable states form a strict subset of entangled states. A natural question
arises concerning how much territory steerability occupies entanglement for a
general two-qubit entangled state. In this work, we investigate the constraint
relation between steerability and concurrence by using two kinds of
evolutionary states and randomly generated two-qubit states. By combining the
theoretical and numerical proofs, we obtain the upper and lower boundaries of
steerability. And the lower boundary can be used as a sufficient criterion for
steering detection. Futhermore, we consider a special kind of mixed state
transformed by performing an arbitrary unitary operation on Werner-like state,
and propose a sufficient steering criterion described by concurrence and
purity.
