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Step one: calculate pixel density, not just resolution
Start with pixels per inch, because the same resolution looks different at different sizes. Divide the diagonal pixel count by the diagonal screen size. Worked example: a 27-inch monitor at 2560 by 1440 has about 109 pixels per inch, while a 27-inch panel at 3840 by 2160 reaches roughly 163. At arm's length, the higher figure renders small text and fine lines with visibly smoother edges. A 24-inch 1920 by 1080 panel lands near 92, which can look slightly soft for text-heavy work. Write the numbers for each candidate in a simple table before comparing prices.
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Step two: match density to viewing distance and task
Next, decide how far you sit and what you do. Close-up document work, coding and photo editing reward higher density because you see individual characters. Video watching from a couch relies more on size and contrast than on extreme pixel counts. Continuing the example, if you sit about 60 centimeters from a 27-inch screen and read spreadsheets all day, the 163 figure is a meaningful upgrade. If you mostly stream shows from farther away, the 109 figure may already look sharp enough. Note your own task and distance, then rank candidates against that, not against a spec headline.
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Step three: check scaling, panel quality and your hardware
Finally, test the practical limits. High resolution often needs operating-system scaling, which can blur older applications, so confirm your main programs look right. Check panel type, brightness, color coverage and refresh rate, since a sharp grid on a washed-out panel still looks flat. Confirm your computer can drive the screen through its ports and graphics output at the refresh rate you want. In the example, the sharper 27-inch monitor needs a compatible connection and capable graphics. Buy from a seller with a fair return window, and view real text and photos for a day before deciding.