What does "Available Space" referst to?

1) Is it the amount of memory that forms created take up? or

2) Is it the amount of memory that file uploads take up? - also are "file uploads" files that the form developer include in the forms? or files that end users include whenever they send a submission for a given form? or

3) Is it the amount of memory that submissions take up? If this is the case, why do I have 305 submissions, however, my profile indicates my upload space is "zero" out of 100MB - because of rounding?

or all of the above?

Another question: I have a form with 305 submissions associated. However, in my profile, it indicates I have used "zero" of submissions out of the 10k limit. The "zero" refers to the fact that I have "zero" submissions in the current month?

Thanks.

Hello again, 

Uploads space will be used if you add a file upload field to your forms for users to send files to you. Forms themselves do not take uploads space. However, if you upload logos or backgrounds to forms, those files can take some space. 

Another question: I have a form with 305 submissions associated. However, in my profile, it indicates I have used "zero" of submissions out of the 10k limit. The "zero" refers to the fact that I have "zero" submissions in the current month?

You are right, 305 is a counter for total submissions that are in account storage. But, for this month you have not received submissions, so monthly counter is zero. Please review this article to better understand account usage: Understanding-Your-Account-Usage-and-Limits