Make a JPEG smaller without wrecking it

What the tool does to a JPEG

Drop your JPEG into the tool on the home page, choose JPEG in the output format control, and press start. The file is read in your browser, decoded to pixels, and encoded again from those pixels. Nothing is uploaded: the encode happens on this device.

The row that comes back is your check on the result. It shows the size you started with and the size you are about to get, whether that is smaller or larger, the pixel dimensions of the output, and a download link. It also shows both pictures side by side, yours on the left and the output on the right, so you can see the difference before you save anything.

You can convert more than one file at a time. The run starts one worker for every core your browser reports, never more workers than there are files to convert, and each worker takes the files one after another. For AVIF output the encoder has threads of its own, so those cores are shared between the encoder’s threads and the files in the batch. A device with little memory starts fewer workers, because each one needs room for a decoded picture and a codec. The cancel button stops the whole run at once. If one file in the batch cannot be converted, that row explains it and the rest still finish.

Choosing a quality

Quality is a whole number from 1 to 100, and it starts at 75. It applies to JPEG, WebP and AVIF, which are all lossy formats: a lower number spends fewer bits on the picture, so the file is smaller and more of the picture is rebuilt from a description rather than kept. Which detail goes first depends on the picture and on the encoder, so this page does not promise an order. What is true of every setting is that the output is a new encoding, not the file you handed over.

If you are not sure where to start, leave it at 75 and look at the two previews. If a lower setting looks acceptable to you and the file is smaller, that is a good trade. The one thing this site will not do is tell you how much detail a given number costs, because that depends on your picture and no measurement on this site would hold for yours. The previews are the measurement you can trust, since they are your own file.

Resizing instead of, or as well as, lowering the quality

Size is the setting that removes pixels without asking the encoder to throw anything away. Turn the resize control from its default of off to one of two modes.

By width sets the output to that many pixels wide, and the height follows from the picture’s proportions, rounded to the nearest pixel. A 3:2 photograph at a width of 1280 comes out 1280 by 853. This is the mode to use when a form, a theme or an email message states a maximum width.

By percent makes both sides that share of the original, so 50 percent halves each dimension. The field stops at 100, so this mode cannot make a picture larger. A width set above the original does enlarge the picture, which is almost never what makes a file smaller, and it is why the percent mode is the safer of the two when you only want to shrink.

One thing to know about dimensions: if your camera stored a rotation in the file, that rotation is applied to the pixels before the resize is calculated, so a photo taken in portrait comes out the right way up. The four EXIF orientations that include a quarter turn, 5 to 8, swap the width and the height, so a file whose numbers read 600 by 400 comes out 400 by 600. The other four leave both numbers as they were, the 180 degree turn among them, since turning a picture does not make it taller or wider. An AVIF input’s EXIF block is not read, so an AVIF file is used as it is stored.

What a JPEG output does to transparency and to metadata

JPEG has no alpha channel. If your picture has transparent areas and you ask for a JPEG, the tool composites what was transparent onto white before encoding, so those areas read as light rather than black. Choose PNG, WebP or AVIF instead if the transparency has to survive.

Metadata goes by default. The output carries no EXIF at all, so camera, device and location data does not travel with the picture. Tick the keep control and the block comes back in a JPEG, a PNG or a WebP output, with the orientation written as 1 because the pixels are already upright. An AVIF output cannot carry the block, and the row says the metadata was not kept rather than leaving the control looking as if it worked.

When a JPEG cannot be made small enough

If you set a target size in KiB, the tool spends quality to reach it: down, as far as 1, when the first encode is over the number, and up from your setting, never past 100, when it comes out well under. Only the upward search is bounded by your setting, so a file that was over the target can come back rougher than the quality you chose. A picture that is still over the target at quality 1 does not reach it, and the row says the target was missed and you get the quality 1 encode. Otherwise the search aims at the band from 95% to 100% of your target and lands in it when a whole-number quality step falls inside it, and it never goes over your number. The verdict is counted on the bytes you download, after any EXIF you asked to keep.

When quality alone is not enough, the number of pixels is what is left. The resize control above removes them without asking the encoder for a lossy reconstruction, and fewer pixels lower the size directly: half the width is a quarter of the pixels. Which change your picture tolerates is yours to judge from the two previews. If the shape of the picture is what matters rather than its detail, resize is the right tool.

If a file is refused

Two fixed limits apply. An input larger than 32 MiB is turned away from its size alone, before its bytes are read. An input over 40,000,000 pixels has to be read in full before its pixel count is known, and is then refused before anything decodes its pixels. Both numbers are fixed rather than a reading of your machine, so a faster or smaller computer does not raise them. What does change them is the input: crop the picture, shrink it elsewhere first, or split the work.

A file that is damaged or truncated gets a row that says so, and the rest of the batch finishes. A format the tool does not read, including JPEG XL and HEIC, is refused in the same way. The tool reads JPEG, PNG, WebP and AVIF.

What to do next

Set a quality, read the two previews, and lower it only if the difference is one you can live with. If the file has to be under a number rather than merely smaller, the target size page explains that ceiling and its two limits. If a picture has to get smaller without any loss of quality, resize it instead of recompressing it.