Assuming you are referring to a home theater projection screen TV, they usually come in two different aspect ratios 16:9 or 4:3. The size of the projection screen TV is measured diagonally from corner to corner and range anywhere from 40-inches to over 100-inches. So a typical 42-inch widescreen TV would have a viewable area of 36.5 inches by 20.5 inches, while a 60-inch widescreen projection TV would have a viewable area of 51 inches by 29 inches. The actual dimensions of the screens vary depending on the manufacturer.