Size comparison: wav versus MP3

How much space do I save with MP3 compression of audio compared to .wav files?

In particular I'm looking for voice recordings, not so much music.

Any benchmark data about this? Links?

It depends on the bitrate you select when you convert the .wav to .mp3. For some basic stats, ripping a CD to MP3, you start out with:

2 channels of 16bit audio at 44.1KHz = 2 x 16 x 44,100 = 1,411,200 bits/sec, or 172kbyte/sec

Traditionally, wav->mp3 conversions were done at 128kbit, or 16kbyte/sec

So, 172 / 16 = 10.75:1 compression

Voice recordings don't need the full 16/44.1 recording spectrum, since human voices generally max out at 8khz mono. For telephone quality, it's 8bit @ 8khz mono, or about 8kbyte/s. Compressed to mp3 at an appropriate bit rate (figuring a normal 10:1 ratio), you end up with 0.8kbyte/sec, or 819.2bytes/sec.