How to compress an image to 100 KB

The short answer

Three things decide how many kilobytes an image ends up as, and they matter in this order: how many pixels it has, what format it’s saved in, and what quality setting the encoder was given. Work through them in that order and most photos land under 100 KB without looking obviously damaged.

Reaching straight for the quality slider is the usual mistake. It’s the weakest of the three levers and the first one to produce visible artifacts, so it should be the last thing you touch, not the first.

Start with the pixel dimensions

File size scales with pixel count, and pixel count scales with the square of the dimensions. A 4000-pixel-wide photo has sixteen times the pixels of a 1000-pixel-wide one, and roughly that much more data to compress. Nothing else you can change moves the number that far.

So the first question isn’t which format to use — it’s how large the image actually needs to be. A photo going into an upload form is usually displayed small, and a photo going into a page column is displayed at whatever that column is wide. Anything beyond that is bytes nobody sees.

In our image compressor, the Resize dropdown caps the longest edge at 1024, 2048, or 4096 pixels. It only scales down — an image already smaller than the cap is left alone, and the aspect ratio never changes. For most images headed for a 100 KB limit, the 1024 px option does more work than every other setting combined.

If the form you’re filling in specifies pixel dimensions as well as a file size, follow its dimensions first and treat the rest of this as fitting under the limit within them.

Then pick the format

Once the dimensions are right, format is the next-biggest lever. WebP is the sensible default: it generally produces smaller files than JPEG at comparable quality and every current browser supports it. JPEG is the safer answer when something on the receiving end may be picky about file types — plenty of upload forms still accept only .jpg.

PNG is the wrong tool here. It’s lossless, which means a photograph saved as PNG will not get anywhere near 100 KB without shrinking the image drastically first. Save PNG for logos, screenshots, and anything needing transparency. AVIF makes the smallest files of all but takes noticeably longer to encode, and it’s a newer format that some older systems won’t accept. Our guide to WebP, AVIF, and JPEG covers the trade-offs in more detail.

Then walk the quality down

The quality slider isn’t a percentage of the original file — it tells the encoder how hard to compress. For photos, somewhere in the 70–80 range usually looks identical to the source on screen while cutting the size dramatically.

So compress once at a sensible setting and read the result. Each row in the compressor shows the original size, an arrow, and the new size, plus how much smaller it came out. If you’re still over budget, drop the quality by ten and press the re-encode button on that row to run it again with the current settings. Two or three passes is usually all it takes.

The compare view is worth opening before you commit. It puts the original and the compressed version side by side so you can check the parts that suffer first — hair, sharp edges, fine text — rather than judging from a thumbnail.

Why there’s no “type 100 KB and go” box

Our compressor doesn’t have a target-size field, and that’s a deliberate omission rather than a missing feature. Encoders don’t work backwards from a byte count: a tool that offers a target size is running the same compress-check-adjust loop internally and picking a quality for you, without showing you what it gave up to hit the number.

Doing it by hand takes a few seconds longer and tells you something useful — whether 100 KB was comfortable at full dimensions, or whether the image had to be resized to get there. That’s worth knowing before you submit it.

Doing it without uploading the photo

ID photos, scanned documents, and portfolio work headed for an application are exactly the kind of files that shouldn’t take a detour through someone else’s server just to lose a few hundred kilobytes. The image compressor runs entirely inside the browser tab — the file is read from your disk, re-encoded on your own machine, and saved back to it, with no upload step anywhere in the chain.