Ideally how many pages are appropriate for a CV? (Consider Entry level & Experienced cases). Explain why?

1. Entry Level: Not more than02 pages.

2. Experienced level: Not more than03 pages.

Employer does not spend for looking a CV more than30 minutes.

I agree with Mr. Saiful Islam Hiron answer for entry level position, but cv goes to04 pages in case of experienced applicant like project manager, engineer, consultant or IT professionals.