Around two to three pages.
The average CV length is around two to three pages. There is no set rule for how long your CV needs to be, but keeping your CV concise and to the point will help hiring managers to digest your information quickly and efficiently.
Keeping the CV relevant is vital. It is common to have a couple of different versions of a CV, tailored towards the industries that you're applying to.
If you're an experienced academic, you may have a long list of achievements that are necessary to the application. It would be fine to add these, even if the list pushes the CV beyond three pages. Alternatively, extra achievements and experiences could be added to a supporting document.