There isn't really an easy answer to that question. Generally speaking, it's a design decision that needs to be made based on your understanding of the business.
Using a gauge chart generally implies that you have an understanding of the upper and lower bounds of a measurement. Hence, a known max, and min.
As an example, let's say you host web sites, and you have a contractual SLA that your average response time will always be below 3 seconds. In your gauge chart, your min would then be 0 (because you can't have a negative average response time) and I might put the max at 4. (which is some reasonable amount above where I clearly know something is wrong)
There is no hard and fast rule which dictates what your gauge maximums, and minimums should be. If the requirement you're working from doesn't stipulate expected control measurement levels, then the gauge chart is the wrong visualization.
It's like the speedometer in your car. What are its max and min? Why do you suppose they were set that way when the car was designed?
