Hooke's law is a principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to that distance. That is: where is a constant factor characteristic of the spring, its stiffness. One of the properties of elasticity is that it takes about twice as much force to stretch a spring twice as far. That linear dependence of displacement upon stretching force is called Hooke's law. Hooke's Law is that which says that how much stress we apply on any body that much strain will be observed on it
. which means
$F$ is the amount of force applied in $N$,
$x$ is the displacement in the spring in $m$
$k$ is the spring constant or force constant.
Hooke's law formula is used to determine the force constant, displacement and force in a stretched spring.