MacOS – Image dimension column in Finder

When in icon view, you can use "Show item info" under view options just as user6124 described.

Yes, but this is not the 'column' view. Thanks, but I knew this already. – Nimbuz (comment)

Column view, however, prefers to show as much of the current file tree path as possible at the price of extra info. You can enable the preview column from view options to show a preview of the selected image along with some basic information (including pixel dimensions) in the rightmost column.

The preview column only shows the info for the selected file (just one).

In list and cover flow views you can add more info columns to the list by right–clicking the list's titlebar and choose the extra data you want to see:

NOTE: The list of extra columns is relative to the folder's location. In order to get the dimensions available, the folder in question has to reside somewhere under ~/Pictures/. (Under ~/Music/ you could choose e.g. artist or album and under ~/Movies/ you could choose length or codecs and so on…)

It looks like this has to do with Spotlight. Finder's knowledge of additional file information is integrated with Spotlight, disabling it, or adding locations to the privacy list will prevent Finder from reporting file information. This includes image dimensions.

If Finder is not reporting "More Info," make sure that directory is not blacklisted by Spotlight. In the screenshot above, anything found in the "Private" folder will show a "--" under the More Info section. This is by design.