Many radio manufacturers claim misleading range distances based on a hypothetical antenna called isotropic antenna. An Isotropic antenna is a hypothetical antenna radiating the same intensity of radio waves in all directions. It thus is said to have a directivity of 0 dBi (dB relative to isotropic) in all directions. However, the range you get from an radio varies based on a lot of factors such as the frequency in use, Atmospheric conditions, Your locations, Radio Power, etc. Modernsurvivalonline.com has a great article regarding ham radio ranges.