How to determine the right screen size for a partucular room size (1 Viewer)

HELLO There

Iam in progress of purchasing runco home cinema projector.I would like guidence for choosing a right size of screen.

My room sixe is 7.00 Meters in length and Width is 3.00 Meters.

The Distance between the screen wall to the seating is 5.5 meters or 6.00 meters.

How do i calculate the size of the screen i should be installing.Iam looking for fixed wall screen.

How up should be distance from ground level the screen should be installed.

Muchly appreciated for the details provided.

Regards
Santhosh

you can get answers to some of your questions by using the viewing distance calculator here.