What WordPress really does with images, measured on this WordPress 7.1.2 site: the files created for each upload and their sizes, the srcset and sizes markup it writes, how AVIF uploads behave on shared hosting, and how much an optimisation plugin could save at equal quality. The workflows in these guides follow from those numbers, so you can check the same things on your own site in a few minutes before changing settings or installing plugins.
Uploading AVIF to WordPress: What Our Shared Host Actually Did
WordPress 7.1.2 accepted our AVIF upload but created no image sizes, and the server sent it as application/octet-stream. Chrome still showed it, by sniffing.
WordPress Workflow 4 min read
When Alt Text Breaks srcset: A WordPress sizes Quirk
WordPress checks for an existing sizes attribute by searching the whole img tag, alt text included. Five of our images lost sizes that way and downloaded full-size files on desktop.
WordPress Workflow 4 min read
Our Theme Lazy-Loaded the First Archive Image: What WordPress Does Instead
Forcing loading=lazy on archive cards overrode WordPress. Letting WordPress 7.1.2 decide gave the first card fetchpriority=high, and it was requested 360 to 500 ms sooner.
WordPress Workflow 5 min read
Cache Headers on a Shared WordPress Host: What Each File Type Gets
JPEG, PNG, WebP, SVG, font and script files on our host were cacheable for a year, but AVIF uploads came with the wrong content type and max-age=0. How to check and fix your own.
WordPress Workflow 3 min read
WordPress Big Image Threshold and the 2048-Pixel srcset Limit
For a 5184-pixel upload, WordPress served at most a 2048-pixel file in srcset, used a 2560-pixel scaled copy as full size and kept the 2.8 MB original on the server, unused by pages.
WordPress Workflow 3 min read
What WordPress Writes When You Upload a Photo: Quality, Sampling and Metadata
On this host WordPress made every JPEG size with ImageMagick at exactly quality 82, baseline, 4:4:4 and without metadata, and its WebP sizes with GD. The 4:4:4 sampling cost 15 to 18 % extra.
WordPress Workflow 4 min read
What WordPress Creates When You Upload a Photo: 3 Uploads Measured
A 2.9 MB camera JPEG left eight files totalling 4,048,293 bytes on our server. The same photo uploaded as a 1600-pixel WebP used 280,622 bytes, 14 times less.
WordPress Workflow 4 min read
WordPress Image Sizes: Which One Does the Browser Actually Download?
With WordPress's default sizes on an eager image, Chrome downloaded a 182 KB file for a 760-pixel desktop column; sizes=auto or a corrected rule took 53 KB.
WordPress Workflow 4 min read
Before You Install an Image Plugin: Measure What It Could Save
At equal quality, converting WordPress's own JPEG sizes saved 5–25 % with WebP and 42–44 % with AVIF in our test. A checklist to run before installing a plugin.
WordPress Workflow 4 min read