How are LCDs Measured

Is it like with TVs, that it says 15" but its less?

screens are measured by bottom(left or right) to top(right or left), now on tv's and crt's it won't be what it says it is because some of the screen is covered by the casing.

they are measured diagonaly, and crts will usually tell you the aactual viewable size.

That depends on the manufacturer. My viewsonic 19 inch has 18 inches that are viewable. Look at some ads on newegg or whatever and you should see both numbers on at least some of them. Also remember that widescreen monitors are measured the same way but the height to width ration is different.

Going back to the 19 inch monitor, it is 10.75 inches high and 14.3 inches wide. My lappy on the other hand has 17 viewable diagonal inches but it is 9.1 inches high and 14.5 inches wide.