The best time to compress a WordPress image is before it reaches your media library. Do it beforehand and you skip the plugin, the API credits and the bloated uploads folder entirely. Preset to WebP at 1920px below.
Preset to WebP at 1920px — compress here, then upload to WordPress.
WordPress generates multiple sized copies of every image you upload — thumbnail, medium, large, and whatever extra sizes your theme defines. A single upload commonly becomes six or more files on disk.
All of them are derived from the original. Upload a 6MB camera JPEG and WordPress dutifully produces six large derivatives of a needlessly large file. Compress first and every generated size inherits the saving, your uploads folder stays manageable, and backups stop taking all night.
ShortPixel, Smush, Imagify and EWWW all work. They are worth it when you have an existing library of thousands of images to fix retroactively, or a team uploading unoptimised files you cannot train.
What they cost you is worth knowing. Most send your images to the vendor's servers for processing, which is a third-party data flow you may not want. Most meter usage, so a bulk optimisation run turns into a bill. And every plugin is more PHP on every request, plus another thing to keep updated and another possible conflict.
If you are the one uploading, compressing beforehand removes all of that and costs nothing.
WordPress has supported WebP uploads since version 5.8, so you can upload WebP directly and it behaves like any other image.
Two things to check. Some older themes hard-code the formats they expect — test one image before converting your whole library. And some managed hosts still restrict WebP at the server level; if an upload is rejected, that is usually why, and support can normally switch it on.
If WebP causes trouble on your setup, compress as JPG instead. A well-compressed JPEG still beats an unoptimised one by a wide margin.
Also worth doing once: prune the image sizes your theme registers. Most define sizes nothing on the site ever uses, and every one of them is generated for every upload forever.
Yes. WordPress generates several sized copies of every upload, all derived from the original, so compressing beforehand means every generated size inherits the saving and your media library stays small.
Not if you compress before uploading. Plugins are useful for fixing an existing library retroactively or for teams uploading unoptimised files, but they add server load, usually send your images to a third party, and often meter usage.
Yes, since WordPress 5.8 you can upload WebP directly. Test one image first — a few older themes and some managed hosts still have restrictions that need switching on.
1920px wide is a safe maximum for full-width images; WordPress will generate its smaller sizes from that. Featured images often want 1200 × 630, but check what your specific theme asks for.