All 24" 1920x1200 widescreen monitors have a .27mm dot pitch.
Let's do the math:
Sqrt(1920^2 + 1200^2) = 2264.15 diagonal pixels
2264.15 diagonal pixels * .27mm dot pitch = 611.32mm diagonal.
611.32mm / 25.4mm/inch = 24 inches.
A 1920x1200 monitor with a .285mm dot pitch would be 25.4" diagonal.
In the past, with analog tube monitors, dot pitch meant how blurry a given resolution would look. Higher monitor sizes and lower dot pitches both meant a sharper image.
With a digital display panel, dot pitch is directly proportional to the size and resolution. It's like squares on a graph paper - to fit a certain amount of squares on a given size sheet of paper, each square has to be a certain size, no more and no less.