Check, measure and switch off image sizes

What is in the list — and where it comes from

The table is not a built-in list, it is the state of your installation: Kakapo asks WordPress itself for the registered sizes and takes the dimensions from the additional sizes or from the core options under Settings › Media. Whatever your theme or a plugin registers in code is therefore included automatically.

The “Crop” column distinguishes two cases: “proportional” means WordPress scales the image down and keeps the aspect ratio; “fixed crop” means it is cropped to exactly these dimensions — if an alignment is stored, it is shown alongside (for example “fixed crop (top left)”).

The “Origin” column is deliberately coarse. For the core sizes the source is stated precisely, everything else is called “Theme or plugin”. It cannot be more precise: when a size is registered, WordPress records nowhere who registered it. A size that you have switched off and that nobody registers any more (typical after a theme change) still stays in the list — with the note “not currently registered”. Otherwise you could never switch it back on.

Measure first, then decide

As long as you have not measured, the “Occupied” column shows a dash. That is intentional: estimated numbers would be worthless here. “Measure now” runs a pass through the uploads folder. Every file is counted with its real size, and the assignment to the image sizes goes through the Media Library — it records for each attachment which file belongs to which size. Going by the file name would not work, because proportional sizes end up with different dimensions depending on the aspect ratio.

The result splits into derived sizes, backups from the image editing (which WordPress keeps itself after cropping or rotating), original image files, files without a matching media library entry, and files that are not images (PDF, ZIP, cache files from other plugins).

There are two special cases in the table you should know about. “shares the file of a size with the same dimensions” means: two sizes have identical dimensions, and WordPress only creates one file for them. That size does not occupy anything of its own, so switching it off saves nothing there either. And “× file missing” means: the Media Library knows this file, but it is no longer on the hard disk.

The measurement runs within a time budget of 20 seconds and reads the Media Library in portions of 200 entries. If the time is not enough on a large stock, the result is marked as incomplete and the numbers are lower bounds — not extrapolated. Then simply measure again. With more than 120,000 image files Kakapo leaves out the breakdown of the remainder into originals and orphans so as not to blow the memory; the remaining numbers stay fully measured.

Switching off: what it does and what it does not

Switching off means: this size is no longer generated. It takes effect from the next upload and when the sizes are generated again after an image edit. It does not work retroactively — this plugin does not delete any image files. Everything that is already in the uploads folder stays there, because the Media Library still points to it and a theme that does use the size after all would otherwise have gaps.

If a page later requests a switched-off size, WordPress delivers the next file that exists, usually the original. The page stays intact, but loads more bytes at that point. That is exactly why switching off pays off above all for sizes that your site does not deliver anywhere anyway.

Four sizes are special: thumbnail, medium, medium_large and large. WordPress itself relies on them — the preview in the Media Library, the choice when inserting, srcset. In the table they carry the note “used by the core itself”, and before you switch one off you get a confirmation prompt. It is not forbidden, you should just know what you are doing.

The most worthwhile candidates are usually the two additional sizes of the core, 1536x1536 and 2048x2048: the 2× variants and thus the largest derived files of all. If your site does not need retina delivery, that is where you save the most. Everything can be undone at any time — “Switch on” puts the size back into service, from the next upload onwards.

Image editing: why switched-off sizes fly out of the entry

If you crop an image in WordPress or rotate it, the core generates the sizes anew and merges the results with the old data. Nothing new is created for switched-off sizes — so their old entry would survive and keep pointing to the file from BEFORE the edit. After a rotation, that size would still deliver the unrotated image; and anyone who picks a crop in order to take something out of the picture would still have it on the web in exactly those sizes.

That is why Kakapo removes the entry from the Media Library data after a real edit. Narrowly limited: only for the edited attachment and only if the main file really has changed (different name or different dimensions). The “thumbnail only” edit stays untouched, and so does every other save. Nothing is deleted here either — the old file stays where it is and shows up in the next measurement under “Without a Media Library entry”.

When something does not look the way you expected

“Dormant” above the list: without a valid license Kakapo does not register the filters in the first place, and switched-off sizes then continue to be generated. In this case the list shows your setting, not what is actually running.

“Uploads folder not found”: the measurement aborts with the path that WordPress reported. Usually the uploads setting is no longer correct or the folder is not readable for PHP.

“The file tree could not be read in full”: a subfolder was not readable or disappeared during the measurement. The run continues, but the result is marked as incomplete, together with the reason. Symbolic links are skipped so that the same file is not counted twice.

“Sizes on disk that are no longer registered”: this lists sizes for which files exist, but which no theme and no plugin registers any more — almost always the trace of a theme change. They are no longer newly generated; you have to clean them up yourself if needed, Kakapo does not touch them.