How should I calculate hardware requirements of a video center web site? [migrated]

I like to create a website like youtube, that I estimate 100K to 1M users for the first month will sign up there. But don’t know how should I calculate the hardware that I need for such website and number of users?

I also have a plan to reach 30M users and 10M viewer per day in the end of first year.

Is there any formula to do rough estimation for hardware requirements?