This is called kerning and just like joojaa said, it's different on every font, UNLESS you are using monospace fonts. In this case, just get the font you're using and simply measure it with any design software such as Photoshop, Illustrator, Figma, whatever.
Now, if your font is NOT monospaced, then you can still measure it, but you'll break the natural kerning of the font. Consider the following image:
As you can see, without kerning applied the letters look almost as if they were for different words. Which means that adding more space will make the problem worse. See image below: I just edited teh regular Google listing and added the following:
and here's the result
almost ilegible and clearly non-accesible text.
In summary: there's not a "cover all cases" answer, but depending on the selected font there can be ways to do this by measuring the space. WHY to do this is a whole different story and I'd strongly recommend you test this extensively