GMRS frequencies have output power than FRS freqs. If your radio has both GMRS and FRS freqs (as most do) the its output will vary depending on which channel that you use.
Radios operating on FRS freqs will put out approximately 500 miliwatts (.5 watt) and will transmit approximately 1.5 miles line-of-sight distance. Normally you will get transmit around 1/2 mile.
Hand-held radios operating on GMRS freqs may put out as much as 5 watts. Base stations may put out as much as 50 watts.
Channels 1-7 are both FRS and GMRS freqs. If you have a radio capable of both FRS and GMRS, then you will transmit at the higher GMRS wattage output. If you have an older radio that only transmits on FRS, then your radio will only transmit 1/2 watt. If you have two different types of radios trying to communicate with each other, then the communication range will be limited by the output of the weaker FRS radio.
Channels 8-14 are FRS only freqs. Even if your radio has GMRS capability, it still will only transmit a maximum 1/2 watt on these channels. Use these channels when your group will operate in close proximity, you don’t want your transmissions traveling too far, and you are practicing communications security (COMSEC).
Channels 15-22 are GMRS only freqs. Your radio will transmit at its full capability (as much as 5 watts). Use these channels with each person in the group has a GMRS type radio and needs to transmit maximum distance.
The advertised range of any radio set is a lie. The range shown on the box is a theoretical best case, line-of-sight scenario. It does not take into account terrain and obstructions that greatly diminish communications range.
Privacy codes do not provide privacy. Any of the codes of one or greater will allow you to only hear other radios using the same channel and privacy code combination. If you use zero as your code then you will be able to hear anyone on your channel, regardless of the code that they are using. Again, privacy codes do not give you any privacy.
If you don’t have the patience for a detailed explanation, then you will still be well served by the information above. If you want to know more, keep reading.