Consider that you're not starting from 'no kerning', but from deliberately bad kerning. The overall width is a given because it tells you the tracking (letter-

Consider that you're not starting from 'no kerning', but from deliberately bad kerning. The overall width is a given because it tells you the tracking (letter-spacing) you're aiming for. It's common for this parameter to be user-selectable even when kerning is completely automatic (or to be automatically adjusted for the purpose of justification), so when you are the kerning algorithm, it's not your job to question that choice. I can see how this can seem weird, as nominally you are responsible for deciding the overall width. But if you had to try to continue the tracking between the first two glyphs instead, or aim for e.g. "+20%", it would be much more difficult. Being able to continuously deal with the feeling of "they want me to do WHAT!?" is one of the skills that distinguishes pro graphic designers from amateurs ;)