See here an easy patch scale conversion tool, I have generated as an outcome of this thread.
Here the related instructions:

I will be happy to improve it based on your comments and suggestions.

EDIT/ADDITION: Working with patches, I have found it useful to have source patches directly in % value. For this reason, I have created a second version using that kind of input.
I have cross-checked it against the outcome of the 16-235 greyscale generated by CS, and the generated values match each other.

Attached file: 0-255 Excel conversion Tool

Attached file: % Excel Conversion tool