File size in Excel

It really depends on additional factors, such as how much FREE memory you have remaining, how long you're willing to wait for a spreadsheet to open up and/or calculate, etc.

I've had spreadsheets that were slightly in excess of 20M before, but that's about it.

However, if you're getting up over 10 or 20 megabytes, you might want to consider looking at a database solution instead. A database might make it quicker to access, and will allow you more than 65K rows.

A decision to move to adatabase is application-specific, but as a general rule I'd take a look at possibly porting it.

I will assume you are asking the question for curiosity purposes only since if you were to push the limits of your available memory by having some 500+ worksheets in your spreadsheet, it would be a bear to maintain.

If you are running with 512kof memory and even are able to give the spreadsheet 1GB of disk space, I would love to know what kind of a spreadsheet would push that limit of worksheets since I've never seen anything of the sort. Certainly anything like that would be better suited for Access or SQL.