How to Optimize Images for WordPress

WordPress has a trick a lot of people don't know about: every time you upload an image to the media library, it automatically generates several copies at different sizes — thumbnail, medium, large — so it can serve the right one wherever it's needed. The problem is that trick has a clear limit: every one of those copies is generated from the same original file you uploaded. If that original weighs 6 MB, the derived copies inherit that excess weight — just at a lower resolution.

Why WordPress doesn't solve this for you on its own

WordPress's sizing system is designed to serve the right image depending on where it's used — a thumbnail in the post listing, the full size inside the post itself — but it isn't designed to intelligently compress the original file. If you upload an unoptimized camera photo weighing 6 MB, WordPress will still dutifully generate its six or seven derived sizes, but the largest of them will still weigh far more than a website actually needs. That's why optimizing before you upload remains a manual step that WordPress doesn't handle by default, even though some third-party plugins add it afterward.

The right order: compress before uploading, not after

Many WordPress image-optimization plugins work "after the fact" — they compress the file once it's already in the media library, which works, but adds an extra layer of processing on the server itself every time you upload content, and on more modest hosting plans that can slow down the upload or even fail with large files. Compressing the image in your own browser before uploading it skips that step entirely: you upload a file that already weighs what it should, without relying on the server to process it for you.

With the SMALLIMG compressor you can adjust quality and maximum width before uploading any image to WordPress. As a reference: for most blog posts or product pages, a maximum width of 1600-2000 pixels is more than enough — WordPress will already take care of generating the smaller sizes from there — and a quality of 80-85% in JPG or WebP keeps the result visually indistinguishable from the original.

Which format works best for WordPress

WordPress has supported WebP natively since version 5.8, so you no longer need any additional plugin to upload images in that format — it typically weighs less than a JPG at equivalent visual quality, which translates directly into a faster-loading site. If your theme or some very old plugin still doesn't support it well, JPG remains the safe, universal fallback.