nitrogen in a closed container due to adsorption of the nitrogen molecules to the surface of the material inserted in the container is measured. Also, the shape of the nanopowder particles is assumed to be spherical. D = 6/(ρ*A) Where "D" is the effective diameter, "ρ" is the density and "A" is the surface area found from the B.E.T. method. See also Characterization of nanoparticles References General references Nanotechnology Metrology