Abstract: Systematic studies of the effect of the electron concentration on the Raman spectra of single-layer graphene films have been carried out. The samples were grown by thermal destruction of the Si-face of the 4H-SiC substrate. Analysis of the results led us to the conclusion that for the correct estimation of the electron concentration and strain values in graphene using Raman spectroscopy data it is necessary to take into account the value of the Fermi velocity in the graphene layer. This conclusion is valid for graphene on any other substrate as well, since the Fermi velocity in graphene depends on the dielectric constant of the substrate.