What size should cold air return grille be?

AllGoNoShow

I am adding a cold air return in my house in the floor. The ducting will be 8 inch round leading back to the main trunk. How large does the grille need to be in the floor to accomodate this duct and not choke anything down?

Also, is it alright to use a grille that is louvered for the return? Or should I stick with the egg-crate type? Thanks for the assistance!

Nick

rakes9720

They need to have the same area (area of 8 inch circle and area of the rectangle grille) so about 200 square inches.