Compress JPG

How do I compress a JPG?

1. Drop one or more JPG files onto the drop zone, or click it to browse.
2. Set Quality. 75 is the default and suits most photos; go lower for email attachments.
3. Optionally set Max width in pixels. Leave it at 0 to keep the original dimensions.
4. Click Compress JPG.
5. Download the result, or use Download all as ZIP when you compressed several files.

Compress JPG decodes each photo with createImageBitmap inside a Web Worker, redraws it on an OffscreenCanvas and re-encodes it as a new JPEG at the quality you choose. JPEG is lossy, so the encoder discards fine detail the eye is least likely to notice, and the lower the quality number the more it discards. Because the work happens in a worker, the page stays responsive while a batch of 50 holiday photos is processed.

Quality 75 is the sweet spot for most uses: a 4 MB phone photo typically lands between 0.8 MB and 1.6 MB, a 60 to 80% saving, and side by side with the original the difference is hard to spot. Use 85 to 90 for prints or portfolio images where you want a safety margin, and 50 to 60 for thumbnails or images that will be viewed small. Below 40 you will start to see blocking around edges and banding in skies.

Max width is the other big lever. A 12 megapixel photo is around 4000 pixels on its longest side, yet most web pages display images at 1200 to 2000 pixels and email clients shrink them further. Setting Max width to 1600 limits the longest side to 1600 pixels while keeping the aspect ratio, and that alone can remove three quarters of the file before quality even comes into it. Leave it at 0 to keep the original pixel dimensions. The tool never enlarges an image.

Re-encoding writes a fresh JPEG, so EXIF metadata such as camera model, capture date and GPS location is stripped as a side effect. That is usually welcome when sharing, but keep the original if you need the data. Colour profile information is not carried across either, so images saved in a wide gamut profile may look slightly different in colour-managed software. Progressive and baseline JPEGs are both accepted.

Nothing is uploaded. The file is read from disk into browser memory, processed there and offered back as a download, which is why there is no size limit beyond what your device can hold in memory and why a 20 MB file finishes in a second or two. Close the tab and nothing remains.

How it works: this tool uses your browser's Canvas and WebCodecs APIs, plus libheif for HEIC. No server is involved, so Kilnfile never sees your file. Last reviewed 20 September 2026.

Frequently asked questions