If your .wav files were made from CDs the current quality your looking at is a little above 1400kb/sec giving you a .wav file of about 40mb. Converting it to "CD Quality" .mp3 format will give you 320kb/sec giving you an .mp3 file of about 9.5mb, saving you about 75% of your disk space. The ratio between kb/sec and file size is exact the only variable is the song length.
320kb/sec .mp3 format is pretty decent. The .mp3 format is known to start clipping audio above about 17000Hz, near the upper end of the human audible range. It does this intentionally to reduce the audio file size to the typical human audible range. If your 20 years old the highest you may hear is around 18,0000Hz to 20000Hz, if you are 40 years old the highest is closer to 17,000Hz, if you are 60 it is around 16,000Hz or less (of course these are just typical results, you may be different). Other than that, useing standard room audio equipment and with ever-present room background noise (i.e. not in a studio environment) can make the difference between 1400kb/sec and 320kb/sec smaller than you would think. So unless your dog (hears up to 45,000HZ) or your cat (up to 64,000Hz) start complaining 320kb/sec is respectable audio quality.
Where you will notice the greatest degradation in sound is from 320kb/sec on down. For instance standard music service downloads (i.e iTunes) at 128kb/sec. Even an untrained ear with a hangover can distinguish the audio difference between 320kb/sec and 128kb/sec pretty quickly.
Some might have known this already but if may be useful to some others contemplating what format to save in and what compression rate to use or download at.