[kekie]

When you're titrating with a strong acid, something with a buffer in it, your graph of pH (on the y axis) and M of acid/time (on the x axis) looks something like this;

Right?

Well, I can figure out a lot of things mathematically, but not the range of the buffer/width of the plateau.
How do I do this?

I would think it would be a function of the M of buffer - maybe a 1:1 ratio? 1M of buffer 'cancels' 1M of acid?

[AWK]

see buffer capacity in: http://en.wikipedia.org/wiki/Buffer_solution

[Borek]

Well, I can figure out a lot of things mathematically, but not the range of the buffer/width of the plateau.
How do I do this?

First of all, you have to define "the range of the buffer" or "width of the plateau". It is not clear what you mean by these.