* 4.0 scale: The highest GPA is a 4.0. This is the most common scale in the US.
* Other scales: Some schools use scales like 4.3, 5.0, or even higher, where extra credit or weighted classes can inflate the GPA beyond a traditional 4.0.
Therefore, there isn't a single definitive answer. A 4.0 is the highest on the most common scale, but higher GPAs are possible on less common scales.