I have a CD collection ripped to mp3 using EAC/LAME alt preset insane. It totals 138GB and every file shows 4 to 1 compression when I hold my mouse over it and get all of the information using dBpowerAMP. I am getting ready to re-rip the entire collection to MAC or FLAC (haven't decided yet) and I am trying to closely approximate how much hard drive space I need. Is this correct?

138GB x 4 = 552GB if I rip to wav
552GB x .7 = 386GB if I rip to wav and convert to MAC or FLAC

I used .7 because I did a couple test rips of my CD's and this is pretty close to an average of the 10 CD's that I ripped and converted to APE. So if my calculations are correct I would be saving about 165GB by converting the wav's to APE or FLAC. Does this sound right? I know there will be a little difference if I choose FLAC but I just want to get a close approximation. I figure it wouldn't be more than 10GB more if I choose FLAC over MAC.

I don't have any experience with FLAC but in MAC I usually get around 68%-75% of original size on the highest compression for a group of albums. It depends a lot on the type of music and I have seen particular albums go as low as 55%. I wouldn't expect much deviancy from 70% as you have done considering you will be getting the average of your entire collection.

It should actually be 4.41, not 4:
16 bits/sample * 2 channels * 44100 samples/sec = 1411200 kbps
1411200 / 320000 = 4.41

So 138 * 4.41 * 0.7 = 426GB (you'll need 40GB more than you calculated).

Glad I asked. Thanks!