The example of baked good on BAKERpedia if for a product at 5.1-5.2 pH and TTA is 3.8-3.9ml. TTA is not expressed in percent.
As is explained on the TTA page: https://bakerpedia.com/processes/titratable-acidity-tta/
pH is an indication of how strong the acid is and TTA is the concentration. Total Titratable Acidity is an analytical method, not a calculation.
One of our sponsors, Puratos, have a great video demonstration of the method on YouTube: https://youtu.be/ZZmwt6Ug-Zg
I hope this helps clarify for you. Please do let us know if we can help further.