Thread:Talk:Requests for comment/Standardized thumbnails sizes/Potential client: Extension:MultimediaViewer/reply (6)

You'll have people with non-retina screens in the 2560x1440 range running those big 27-30" monitors.

You'll also have people with retina screens where the screen density bumps you up from 1280x800 or 1440x900 CSS pixels to 2560x1600 or 2880x1800.

Common densities are going to be in the 1.0, 1.5, and 2.0 ranges, but others may appear (especially if you have a funny zoom, etc)