This is so frustrating. I appreciate everyone's answers, but I already have Stock by Attribute installed, and I already have each size as an attribute. Unfortunately, that does not answer my question. How do I assign each size it's own inventory? I really need this spelled out for me I guess.

There is a code edit here from Grayson, but the file that we are told to edit is include/modules/pages/product_info/main_template_vars_attributes.php and that does not exist in my file directory. I found something on Wikipedia that states:

This is relatively straightforward if you have only a single attribute such as size of color for each product. Code for this is proposed in this archive thread[1]. Seek out post #110 by Grayson, and her correction in #132 and apply the changes to the includes/modules/attributes.php file instead of includes/modules/pages/product_info/main_template_vars_attributes.php

Of course, the code we are supposed to change does not exist in that file! And the site keeps giving the message: The connection has timed out. The server at www.zen-cart.com is taking too long to respond.

This seems as if it would be an obvious thing to do, but it is not obvious to me. Can someone walk me through it, please?