Well, the simple answer is 8MB , but the actual answer is you can upload files of any size minimum than your available storage limit.
Suppose you are allotted with a 1000 MB of storage then you can upload a single file of 999 MB if you wish to.
In most cases you’ve noticed a limit of upto 8MB (probably in wordpress Theme or plugin upload) but thanks to MultiPHP INI editor, we can configure the limit to anything we wish.
We can change post_max_size , and upload_max_filesize as per our requirement.
By the way we are allowed to upload a file of any size from cpanel File manager without changing these settings.