We know that,Spring constant is a constant or term that is often used in Hooke’s law, which states that a particular force is needed to extend or compress a spring by some specified distance which when scaled linearly with respect to that distance comes out to be , where is the constant factor and is known as the spring factor .
Since the spring constant is a measure of the stiffness of the spring.
If the spring constant of a coil is to be calculated which is made of a wire of diameter then relation between spring constant and Diameter of coil is given by, (where, is modulus of rigidity, is diameter of wire, is diameter of coil, and is number of active coil).
Therefore if the diameter of coil is large the spring will be stiffer because the spring constant is inversely proportional to the diameter of the coil . With an increase in the diameter of the coil , the spring constant will decrease.