How do I calculate the size of a decompressed file?

For compressed files, how can I calculate the "x" value and use it effectively for the option Size of decompressed file is "x" times the size of compressed file?

This function prevents ScanMail from scanning a compressed file that might cause a Denial-of-Service (DoS) attack. A DoS attack happens when a mail server's resources are overwhelmed by unnecessary tasks. Preventing ScanMail from scanning files that decompress into very large files helps prevent this problem from happening.

Example: For the table below, the "x" value is 100.

* ScanMail takes the action you configure for unscannable files.