When a value is too high to be measured, you can say that it's "off the charts". For example:

The last earthquake was pretty bad, but that one we had five years ago was absolutely off the charts!

To understand this phrase, imagine that you made a graph or chart of all of the normal values of something, like the strengths of all the earthquakes that have occurred in a region. An "off the charts" value won't be able to fit onto the graph.

You can also say that a value is "off the scale".