The stiffness of spring is a measure of its resistance to deformation when a force is applied, it quantifies how much the spring compresses or extends in response to a given load. And is denoted by k. Stiffness of Spring is usually measured using the Newton per Meter for Surface Tension. Note that the value of Stiffness of Spring is always positive. Typically, the value of Stiffness of Spring is greater than 0.