Use this calculator to calculate coil area result in physics.
Formula
$ Z = -2\sqrt{\varphi D \tau t} * \left [ erf^{-1}(2-C/C_{o}) \right ] $
Where,
C = concentration at z
Co = initial concentration
z = distance from the source
p = porosity
D = coefficient of molecular diffusion
t = tortuosity
t = time