Range is a very difficult thing to determine because it can be affected by a great many variables such as trees, buildings, terrain etc.
This is because radio waves travel in straight lines, very similar to light waves and cannot bend although they can be reflected and in some cases bounced.
For example some radios may be able to talk to each other from hilltop to hilltop across 20 miles, however if there are tall buildings or woodland in the way of two radios at a lower level they may not manage a distance of 500 yards.
Therefore it is important for aerials to be kept in a vertical position and the higher the radio is held the more chance of the range being greater. The human body can also be a factor in range, if you’re using a headset and have the radio attached to your belt, the body can act as a shield and reduce the range. There are ways to increase your range such as maybe moving from and unlicensed radio to licensed or utilizing a Local or Talkthrough base station which are all available through walkie-talkies.com.