Convert JPG to WebP

Open a JPG above and the editor exports it as WebP at quality 80, encoded on your device. The output size and the saving against your original appear as soon as it finishes, and the divider lets you compare the two before you download.

WebP is usually described as a quarter to a third smaller than JPEG. For a photo that is already a JPEG, that is not what we measured. This page shows what converting really saves, and when it saves nothing.

What the conversion saved, measured

Our sample is a 1920 × 1280 JPEG of a lakeside landscape, 613 KB as it comes. We exported it through the editor’s own encoders at five slider positions:

Slider	As JPEG again	As WebP	WebP against the 613 KB original
60	300.9 KB	290.0 KB	53% smaller
70	337.5 KB	325.9 KB	47% smaller
80	538.2 KB	423.2 KB	31% smaller
90	655.4 KB	648.7 KB	6% larger

At the default of 80 the WebP is 31% smaller than the file you started with, and that is the number the editor will show you. But look at the middle columns: at the same slider position, WebP and JPEG come out within a few percent of each other everywhere except 80. Most of the saving in that last column comes from choosing a lower quality, not from the change of format. Re-saving as a JPEG at 70 would save nearly as much.

At equal quality, the gap is smaller still

Slider numbers are not comparable between formats, so we measured properly: every export decoded and scored against the source by SSIM, a standard measure of how closely one image matches another, and each JPEG paired with the WebP that scores the same. The script is scripts/measure-webp-vs-jpeg.mjs.

JPEG quality	JPEG	WebP of equal quality	WebP saves
50	273.8 KB	225.7 KB	18%
60	300.9 KB	254.4 KB	15%
70	337.5 KB	268.7 KB	20%
80	538.2 KB	528.6 KB	2%
90	655.4 KB	909.9 KB	−39%

At ordinary web qualities WebP is 15–20% smaller for the same look. Above JPEG 80 the advantage disappears, and matching a JPEG saved at 90 takes a WebP 39% larger.

The same test on our screenshot sample, which was never a JPEG, gives the figures you usually hear: WebP 25–35% smaller than JPEG at every quality from 50 to 95.

Why a JPEG resists being converted

A JPEG stores a picture as 8 × 8 blocks of frequency coefficients, rounded off to save space. Its pixels carry that rounding forever. Re-encoding them as JPEG at a similar quality lines up with the same block grid and rounds the same way, so it reproduces the file almost exactly: our sample re-saved at JPEG 85 scores 0.996, close to identical.

WebP divides the picture differently and has to describe the first encoder’s rounding as if it were detail. At high quality it spends bytes faithfully copying artefacts, which is why the last row goes negative. At moderate quality both formats are throwing detail away anyway, and WebP’s better prediction wins its 15–20%.

When converting is worth it

For a web page, yes: at quality 70–80 the WebP is smaller than any JPEG of the same look, and every current browser shows it.
To archive or edit later, no. Keep the original JPEG. Converting cannot add quality, and every re-encode loses a little more.
Above quality 85, do not expect a saving. If you need the file near-perfect, the original JPEG is already the efficient choice.
For the most saving, use AVIF instead: the same sample at slider 80 is 349 KB as AVIF against 423 KB as WebP. JPG to AVIF has its measurements.
Convert from the original, never from an earlier conversion, so each copy pays for one generation of loss and not two.

Questions about converting JPG to WebP

How much smaller is WebP than JPG?

For a photo that starts as a JPEG, about 15–20% at the same quality, measured at JPEG qualities 50 to 70. Above 80 the saving disappears. For images that were never JPEGs, such as screenshots, it is 25–35%.

Does converting JPG to WebP lose quality?

A little, as any re-encode does. At quality 80 the difference is hard to see on a photo; use the comparison divider to check before you download, and keep the original.

Why is my WebP bigger than the JPG?

Because the quality was set high. Matching a JPEG saved at 90 needs a WebP 39% larger in our test. Lower the quality to 80 or below and the WebP is smaller.

Is the photo uploaded to convert it?

No. The browser decodes the JPG and encodes the WebP on your device, and the file is saved from there. The privacy policy shows how to confirm nothing is sent.

More image tools

Every one of these is the same editor, opened for a different job — and all of them run on your device.

Or start from the full editor, which does all of it at once.