Worksheet size
65,536 rows by 256 columns
Such things can be found in HELP
index tab, specification
If you mean the size of the entire workbook in bytes then
you will not see a limitation there, so it is unspecified.
Which simple means there are no definitive limits. Basically
limitations are imposed by external things like available
memory, available disk space, operating system,
other specification limits.
There are probably some practical limits. The larger the
file the more things will slow down, when a calculation, or a save
is performed.
