Hi
I am a previous user of Point and Shoot camera (Canon Powershot series) and recently shifted to canon EOS 80D. In Shutter Speed Priority Mode, we adjust Shutter and ISO and camera adjusts the Aperture. Higher the Shutter speed would require higher the ISO, otherwise, the picture would be darker.

I tried to set it in Live View, but sometimes Live View is not accurately understandable in some environments.

Is there a formula to quickly calculate ISO according to shutter speed we set?