The fact of the matter is that describing FRS or GMRS by their “mile range” is completely useless. The radio’s range will depend on the specific terrain and circumstances of that particular radio’s usage. A better description would simply be the transmit power in wattage. Your better FRS and GMRS radios will have ˝-watt power on an FRS channel and 5-watt power on a GMRS channel. These are the upper limits set by the U.S. FCC for these types of radios. (Other countries, e.g. Canada, may have different maximums.)

Generally, 5 watts of transmit power from one radio will have about an equal range of 5 watts from another radio for any given terrain.
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“Hiking is just walking where it’s okay to pee. Sometimes old people hike by mistake.” — Demitri Martin