In-browser image optimizer
Compress images for WordPress
WordPress stores the original you upload and derives every other size from the largest one, so a 4000-pixel photo becomes eight large files instead of one. Resizing before upload is the single biggest win, and it costs nothing once you know the sizes your theme actually asks for.
Prepare an image for the media library
- Find the largest size your theme rendersUsually the content width times two for high-density screens: 1600–2000 pixels for a modern block theme. Anything above that is stored and never served.
- Resize, then encode to WebPWordPress has supported WebP in the media library since 5.8. Quality 82 is a safe default; check the thumbnail sizes it generates afterwards.
- Upload the optimised file, not a plugin passOptimisation plugins re-compress what is already there. Starting from a good file means you can skip the plugin, or leave it on “lossless only”.
Why the upload size matters more than the plugin
A single 4000×3000 JPEG in the media library can occupy 15–25 MB once WordPress writes thumbnail, medium, medium_large, large, 1536, 2048 and the theme’s own sizes. Uploading at 1600 pixels cuts that to a few megabytes and makes every generated size smaller too.
WebP, AVIF and the fine print
WebP is stored and served natively now, which makes it the safe choice. AVIF is accepted by newer WordPress versions but the media library cannot generate a fallback automatically — if you serve AVIF, do it through a plugin or <picture> with a WebP source. And unless you have configured a CDN that converts on the fly, keep the original format as the fallback.
What to expect
| WordPress size | Typical dimensions | Note |
|---|---|---|
| thumbnail | 150 × 150 | cropped square |
| medium | 300 px wide | archive grids |
| large | 1024 px wide | most themes |
| 1536 / 2048 | scaled versions | generated for big screens |
| full | whatever you uploaded | so upload smaller |
Themes add their own sizes on top of these, which is another reason to start from a sensible maximum.
Questions
What image size should I upload to WordPress?
The largest size the theme renders, doubled for high-density screens — usually 1600–2000 pixels wide. Uploading more only fills the media library with files nobody downloads.
Does WordPress support WebP?
Yes, since 5.8 the media library accepts and serves WebP, including transparency. Older browsers are rare enough that most sites can ship WebP directly.
Should I still use an optimisation plugin?
If you upload files that are already properly sized and encoded, the added value is small. Lossless-only settings avoid stacking a second lossy pass on your images.