How to Get Nanoparticles Layer Thickness?

Here is an example:

Nickel (Ni) Nanoparticles / Nanopowder (Ni, 99.9%, 20nm, carbon coated, metal basis)
Nickel Nanoparticles (Ni coated with carbon, C = 3.61wt%, O<0.3%)
Carbon Layer Thickness = (1/3)(Particle Radius)(Ni density/C Density)(C wt%)=(1/3)(10 nm)(8900/2267)(3.61%)=0.47 nm