There are some things you need to take into account when assessing the size of a monitor. Sizes are normally stated as a single number, the width of the monitor in inches. In reality, monitor screens are never the size that their manufacturers claim them to be. And this doesn't take into account the fact that the screen image usually has black borders around its edge. Many companies are getting better about advertising the viewable size along with the nominal size, but many still do not.
Some unscrupulous ones exaggerate the stated viewable size of the monitor as well.
I personally find the whole matter of selecting monitors by their diagonal width to be confusing and rather silly. What really matters in the case of a monitor is the viewable surface area . It should be read by looking at the row corresponding to the nominal size of the monitor under consideration. Then, the percentage value in each column is the percentage larger or smaller that size's surface area is compared to the other sizes. Therefore, your real image size will be smaller still than the viewable size of the monitor.