Top Tip: A quick "guestimate" for standard HDTV format screens would be to take the screen
height calculated above and double the number to get a minimum diagonal screen size.
48 I ICT TODAY
16/9 aspect ratio = 1.78 (HDTV standard)
4/3 aspect ratio = 1.33 (NTSC standard)
2.35/1 aspect ratio = 2.35 (Cinemascope standard that is used in libraries, for example). See Figure 2.
STEP 4: Determine the aspect ratio (AR) and screen width. The AR is the ratio of width (W) to height (H).
The most common AR of displays or projection screens in use today is 16 x 9.
STEP 5: Calculate the required display or screen diagonal size using the Pythagorean Theorem. For any right
triangle the diagonal or hypotenuse is equal to the square root of the sum of the sides squared (Figure 3).
FIGURE 2: Three common display aspect ratios.
NTSC Cinemascope HDTV
For a 16 x 9 or 1.78 aspect ratio, screen width equals 1.78 X screen height or Height X 16/9.
EXAMPLE:
Screen width = 1.78 X 40 = 71.2 inches (180.8 cm).
EXAMPLE:
H = Minimum screen height = 40 inches
W = Screen width = 71.2 inches
D (Diagonal) = √(40
2
+ 71.2
2
) = 81.6 inches
(207.2 cm)
Thus, an 85-inch class, 84.6-inch diagonal
(215 cm) display would be required.
FIGURE 3: Use the Pythagorean Theorem to find the
screen diagonal size.
For both projectors and displays, the effect of ambient lighting impacts the selection. Most manufacturers
offer services and support materials to help select the best arrangement, type of display or projector, and
screen depending on environmental factors.
