In the United States, the dimensions of a screen are customarily given in this order:   width first, then height.   However, you may deal with a person or company which uses the opposite system:  height first, then width.  So unless you know that both you and the other party use the same system, it would be prudent to clarify the matter by saying it the way CG Fleissner did:  5 meters wide by 4 meters high.