This standard applies to the method for determining the size of nanoparticles in the range from 5 to 200 nm in gaseous media by their diffusion coefficient. The method is applicable for the analysis of aerosols with a unimodal particle size distribution. The method is implemented using analyzers, the main element of which is a multistage grid-type diffusion battery for separating aerosol particles by size. Each stage of the diffusion battery is a set with a different number of wire meshes. The standard does not prescribe specific methods for measuring particles in specific gas environments.