Have you ever threatened somebody that you're going to count to three and if they didn't listen to you they'll be in a world of trouble?
It goes like this: one... two... ... ... two and a half... two and two-thirds...
The warp scale is lineal from Warp 1 to Warp 9. From there, since they can't get to Warp 10, there always has to be a "faster speed", so they basically top off at 9.5, then 9.6, 9.7, 9.8, 9.9, like what happened in Star Trek IV: The Voyage Bombs where Sulu is counting the warps. Then they cut it down more, 9.91, 9.92, 9.925, 9.9725.
So it's that simple!
