I know this is going to sound simple...but I did a search and didn't find it. How do I find (other than sheer experimentation) my different rep maxes?

I know my one rep max...but the program I just started from this site (Total Body Training by Chad Waterbury) switches reps and set totals a LOT.

So while I know my five rep max, I don't know my 8 rep max, or 12, or 18 (!!)...

Now, I know I could do it simply with experimentation, but I'm worried that this program changes so much that for the first few weeks would simply be experimentation (damn, too light, damn -- to heavy) and I wouldn't be achieving results so much as FINDING the correct totals.

So is there any type of formula (generally speaking) that I could work backwards on?

There are formulas. They are poor.

Guess and check is the only way I have found effective for determining my rep maxes. Do it, if it feels light add some weight, if too heavy take some off.

FWIW (all these based upon my own experience of my 1RM):
90% is 3RM
80-85% is 5 RM
60% is 20RM

Luthar, you can just pick a 3RM, 5RM, that you feel is good for you. You don't really need to find the perfect 3RM, 5RM, etc.

Once you start on a program, after a month your RM will go up and in 4 months you will be warming up with your old RMs.

Thanks for the replies. As for the formulas being poor...at least it gives me a place to start (especially with 12 and 15 RM).

Funkhauser -- you are 100% correct. I've been training (is that what it's called) for four months and guess what? My warmups are my old RMs. Very cool!

I can do things I never thought possible (don't laugh...but like chin ups. I couldn't do any in April...now I can do 3 sets of 5. Cool!).

I LOVE this site.