If you see an LCD television advertised as having, say, a 32-inch screen, that doesn't mean it's 32 inches wide or 32 inches tall. Rather, the 32 inches is the diagonal measurement of the screen, from one corner of the visible area to the opposite corner. TV screens have long been measured this way.

### Background

In his 1990 book "Why Do Dogs Have Wet Noses?"--in which he answered dozens of questions about everyday items--author David Feldman tried to track down why TV screens are measured diagonally. The answer came from Scott J. Stevens, a patent lawyer for Thomson Consumer Electronics, a subsidiary of General Electric. Stevens said it boils down to marketing tactic: The bigger the number given as the measurement, the bigger the screen consumers think they're getting. And measuring the screen diagonally gives a bigger number than measuring either width or height.

### Screen Dimensions

Modern LCD screens have an "aspect ratio" of 16:9. That means the ratio of the screen's width to its height is 16 to 9. A "46-inch" LCD screen, for example, is actually 40.1 inches wide and 22.6 inches tall. (The math 40.1 divided by 16 gives you 2.51, and 22.6 divided by 9 also gives you 2.51). The proportion holds true for any modern LCD screen size. A 32-inch screen, for example, is about 27.9 inches wide by 15.7 inches tall (27.9 / 16 = 1.74, and 15.7 / 9 = 1.74). A 52-inch screen measures 45.3 inches by 25.5 inches (45.3 / 16 = 2.83, and 25.5 / 9 = 2.83).

### Comparisons to Older TVs

Older TV screens have an aspect ratio of 4:3. They're more "square" than the modern widescreen models. Under this aspect ratio, a screen that's 40 inches wide--roughly the same width as a 46-inch LCD screen--would be 30 inches high (40 / 4 = 10, and 30 / 3 = 10). The greater height produces a viewing area one-third larger than the 16:9 screen of the same width--1,200 square inches vs. about 900 square inches. This matters when attempting to compare the screen sizes of a modern LCD TV to that of an old-fashioned 4:3 TV. Whereas a 32-inch screen at 16:9 has dimensions of 27.9 by 15.7 inches, a 32-inch screen at 4:3 has dimensions of 25.6 inches by 19.2 inches. Total screen area for the LCD: about 438 square inches. Total screen area for the old-style TV: about 491.5 inches. Even though these screens are the "same size"--32 inches--the LCD screen is actually about 11 per cent smaller.

### Picking an Equivalent Size

A better way to comparison-shop between modern 16:9 LCD TVs and older 4:3 models may be to go by the height of their respective screens, not the diagonal measurement. If you've been using an older 32-inch screen, then you're accustomed to watching a picture that's a little over 19 inches tall. To get an equivalent-sized picture, you would have to go with a 40-inch model in a 16:9 ratio. That screen will be about 19.6 inches tall.