To charge by the word, or by a character-based measure? The “line” of 55 keystrokes is of course the one I use, but there are other systems – it should be possible to convert precisely through a simple multiplication.
Why mention it again? Because on a recent large job I noticed that the translation process sent the word count up by no less than 35%, representing an uncertainty that neither the client nor the translator is likely to be comfortable with. Contrast this with the character-based measure of size. Measured that way, the text also changed size. It shrank. By well under 1%. I suggest that neither the client nor the translator is likely to be troubled by that.