From the Club 100 support files (www.club100.org)...

HOW MUCH RAM DO YOU HAVE?

The Model 100 was initially sold in 1983 as an 8K RAM machine.  It was and is 
expandable to 32K using 8K RAM Modules--more than just a chip.  Today, you can 
find Model 100s in 8K, 16K, 24K and 32K configurations.  The 8K RAM Modules 
are available from only one source, Club 100 at www.club100.org. 

First of all, you need to dump everything out of RAM.  This is called a cold 
start.  The fastest way to do this is to turn the machine OFF.  Hold down on 
the ctrl and break/pause key, and while holding the two keys, turn the machine 
ON. 

The Model 100 uses some of the RAM for internal operations, so the byte count 
is 3130 bytes less than the RAM count.  A kilobyte (K) = 1024 bytes.  Here are 
the calculations: 

32 x 1024 = 32768 less 3130 = 29638 bytes free
24 x 1024 = 24576 less 3130 = 21446 bytes free
16 x 1024 = 16384 less 3130 = 13254 bytes free
8 x 1024 = 8192 less 3130 = 5065 bytes free

This code comes from Ron Wiesen, an extremely knowledgeable member of Club 100 

There is an easy way to tell the installed RAM in a M100 or T102. Invoke 
BASIC. Type the following statement and press Enter. 

?(256-PEEK(-1343))/4"K

The RAM capacity in Kbytes is reported on the screen. You'll get one of four 
reports: 

8 K 
16 K 
24 K 
32 K