Leaf Spring Formula:
k=8Enbt³/3l³
where,
E = Youngs modulus [Nm^-2]
n = Number of leaves
b = Width of leaves [m]
t = Thickness of leaves [m]
L = Span [m]
Spring Rate is half the difference between the loads 1 inch above and 1 inch below a specified position. This tool will help you dynamically to calculate the Leaf springs stiffness online.