I use calibration solutions for that purpose myself.
Since I'm measuring the pH in my reactor I calibrate with 7 and 4. Two 500ml bottles of solution cost me $15. That lasts me until the expiry date on the solutions - about 4 years.
The way to be sure kalk is saturated is to test the pH. I don't think it is a good calibration solution. But to answer the question, it is 12. I think you should buy some solution. HTH
I have some 7.0 solution, was just wanting to verify the top end. some probes can drift at the top. I had once seen that limewater was used as a calibration medium for high Ph.
