This conversion is almost always about page speed. WebP reaches the same visual quality as JPEG in roughly 25–35% fewer bytes, and every browser in current use can display it, so swapping a site’s photographs over is one of the cheapest performance wins available. If you are chasing a Core Web Vitals score or trying to get a slow product page under control, this is usually the first thing to try.
Where the saving comes from
JPEG was finalised in 1992 and its compression maths reflects that. WebP borrows from modern video coding: it predicts each block of pixels from its neighbours and stores only the difference, and it uses a smarter entropy coder for what remains. On photographs the improvement is consistent. On flat graphics and screenshots it is dramatic — often 50% or better — because WebP handles large single-colour areas far more gracefully.
You are re-compressing an already-compressed image
Worth being straight about: your JPG has already lost detail, and WebP encoding will lose a little more on top. In practice this rarely matters, because WebP at quality 80 usually looks better than the source JPEG did while being smaller. But it does mean two things.
- Do not use this as an archival step. Keep the original JPG, or better, the original camera file.
- Do not run the result back through another lossy conversion. Each round adds damage that the previous round hid.
- If the source JPG was already heavily compressed, WebP will faithfully preserve its artifacts — quality settings cannot repair them.
Choosing a quality level
WebP quality numbers are not interchangeable with JPEG ones. WebP at 80 is roughly comparable to JPEG at 90, so if you convert at the same number you used for JPEG you will usually be over-spending on file size. Start at 80, look at the result, and only move up if you can see a difference at full size. Below about 65, WebP starts smoothing fine texture — skin, fabric, foliage — in a way that reads as slightly plastic.
Where WebP still gets rejected
Browser support is complete, but the wider world lags. Some print services, older desktop software, a few phone gallery apps and certain upload forms still refuse .webp files. Email clients generally display them fine now but recipients on old software may not. If a file is going to a person rather than a web page, JPEG remains the safer choice.
Metadata is dropped in the process. EXIF fields including GPS coordinates and camera settings do not carry across, which is generally what you want for images going onto a public website. Colour is converted to standard sRGB, so an image in a wide-gamut profile may look very slightly different — usually invisible for web use, occasionally noticeable in saturated reds.
The encoding is done by your own browser, in this tab. Nothing is uploaded, so you can convert an entire folder of client photographs without any of them leaving your machine.