You're mixing apples and oranges.

The wattage tells you how much power the radio transmits with. It tells you absolutely nothing about its reception.

However, the more power the guy you're talking to is transmitting with, the more likely you are to hear him, generally speaking.

Now, I'm putting on my Nomex flame-proof suit for my next comment.

The consumer-grade of these radios are toys, period. Their antennas tend to have negative gain (they are what's called a "dummy load") and are generally not replaceable. Antennas are among the most important component on a radio. I can hit distant repeaters on 1 watt with a good antenna that are unreachable with 5 watts and a crummy one.

They also have a vast array of incompatiable subaudiable tones for "privacy" (they have no privacy) and their marketing is full of outright lies. And they almost never, if ever, come even remotely close to their advertised range, even given the most perfect environmental conditions.

I think these radios are great for kids to play with or for communicating between cars following one another on the highway, but outside of very limited domains, I think the consumer models of these radios should be absolutely avoided for any serious purpose.

If you really want one, get the professional GMRS models made by Motorola, not the ones you'll find at Walmart. I believe someone recomended some models earlier in this thread.