by width they mean the width of your monitor plus one and a half to 2 inches, the reason, tho im not certain but believe, is because u could stick a 13 inch tv in it if u wanted, or a 32 inch tv, so the width would always be different, i am also building an ultimate arcade 2, my 27 inch tv was 25 inches wide, so the width of all my peices were 27, hope i helped, thanks.