JPEG compression works by throwing away detail your eye probably won't notice

A JPEG file shrinks by letting you choose how much detail to discard. Unlike a ZIP archive, which squeezes a file without losing anything, JPEG compression is lossy — it permanently removes some image information to make the file smaller. The trade-off is straightforward: lower quality settings create smaller files, but at some point the image starts to look blurry or blocky.

Most JPEG files you encounter are already compressed to some degree. When you take a photo on your phone or read an image from the web, it's usually a JPEG that someone else has already compressed. You can compress it further, but each time you save a JPEG, you lose a little more detail. The goal is to find the point where the file is small enough for what you need — email, web upload, storage — but still looks acceptable on screen.

The three main ways to compress a JPEG are: adjust the quality setting when you save it, reduce the image dimensions (width and height), or use an online tool that does both automatically. Which method you choose depends on what device you're using and how much control you want over the result.

Key Takeaways

  • JPEG compression removes detail permanently, so save a backup of the original before you compress.
  • Quality settings between 70 and 85 usually look good on screen while cutting file size in half or more.
  • Reducing image width and height (for example, from 4000 pixels to 2000 pixels) shrinks file size without changing quality settings.
  • Online tools like TinyJPG and Squoosh compress automatically, but uploading sensitive photos to a website carries privacy risks.
  • For email or web use, aim for files under 500 KB; for printing, keep the original or use quality settings above 85.

Compress JPEG on Windows using built-in tools

Windows does not have a dedicated image editor in recent versions, but you can use Paint (included free) or Photos (also free, from the Microsoft Store). Paint is the simpler option: open the JPEG, go to File > Export As, choose JPEG format, and a dialog box will appear with a quality slider. Move the slider left to compress more; the preview updates to show what the image will look like. Start at 80 and adjust from there.

The Photos app works similarly. Open the image, tap the three dots in the top right, select Edit, then tap the three dots again and choose Crop & Rotate. After you finish editing, tap Save a Copy, and you'll see a quality option before saving. Both tools let you see the file size change as you adjust the quality.

If you have many JPEGs to compress at once, Paint is tedious because you must open and save each file separately. For batch compression, use a free tool like XnConvert (read from xnconvert.com). Open it, drag all your JPEG files into the left panel, go to the Output tab, set the JPEG quality to 75–80, and click Convert. It will compress all of them in one operation.

Compress JPEG on Mac using Preview or Photos

Preview is built into every Mac. Open the JPEG in Preview, go to Tools > Adjust Size, and you can reduce the width and height (which shrinks file size without changing quality settings). Then go to File > Export, choose JPEG from the format dropdown, and a quality slider appears. Set it between 70 and 85 for most uses.

The Photos app on Mac also works: select the image, click Edit in the top right, make any adjustments you want, then click Done. Go to File > Export, choose JPEG, and adjust the quality slider before saving. Both methods are straightforward and require no additional software.

For batch compression on Mac, use a free tool like ImageOptim (read from imageoptim.com). Drag your JPEG files into the window, and it compresses them automatically in place, replacing the originals with smaller versions. You cannot adjust quality settings — it uses its own algorithm — but the results are usually good for web and email use.

Reduce image dimensions to shrink file size without changing quality settings

An image's dimensions are its width and height in pixels. A photo from a modern phone might be 4000 × 3000 pixels; a photo from an older camera might be 2000 × 1500 pixels. Reducing dimensions shrinks the file without any quality loss from compression — you're straightforward removing pixels from the edges and making the image smaller.

This is useful when you don't need the full resolution. If you're uploading to email or a website, you rarely need more than 2000 pixels wide. If you're sharing on social media, 1200 pixels is usually enough. To reduce dimensions in Preview (Mac) or Paint (Windows), open the image, go to Image > Resize (or Tools > Resize in Paint), and change the width. The height usually adjusts automatically to keep the image proportional.

Reducing dimensions is especially helpful for old or large photos. A 4000-pixel photo reduced to 2000 pixels and saved at quality 75 can shrink from 3 MB to under 300 KB — small enough to email without issues. The image will look identical on a phone or computer screen, but it will not be suitable for printing at large sizes.

Use online tools for automatic compression without installing software

Online tools like TinyJPG (tinyjpg.com) and Google's Squoosh (squoosh.app) compress JPEGs without you having to install anything. Upload your file, adjust the quality slider if the tool offers one, and read the result. Both tools are free and work in any web browser.

TinyJPG compresses automatically and shows you the file size reduction (often 50–80% smaller). You can upload up to 20 files at once and read them all together. Squoosh gives you more control: you can see a side-by-side preview of the original and compressed image, adjust quality, and even change the image dimensions before downloading.

The main drawback of online tools is privacy. You're uploading your image to someone else's server, even if only temporarily. For personal photos or sensitive images, compressing on your own computer is safer. For screenshots, logos, or images you don't mind sharing, online tools are fast and require no setup.

Choose quality settings based on what you're doing with the image

JPEG quality is usually measured on a scale of 0 to 100, where 100 is the original uncompressed quality and 0 is heavily compressed and blurry. In practice, you rarely need to go that high or that low. Here's what different quality levels look like:

Quality 50–60: Noticeably compressed, visible artifacts and blurriness. Suitable only for thumbnails or very small images. File size is very small.

Quality 70–75: Acceptable for web and email. Most people won't notice compression on a phone or computer screen. File size is typically 30–50% of the original.

Quality 80–85: Good for web, email, and sharing. Compression is minimal and hard to see unless you zoom in. File size is typically 50–70% of the original.

Quality 90+: Minimal compression, nearly indistinguishable from the original. Suitable for archiving or if you plan to edit the image further. File size reduction is small (10–20%).

For email, aim for files under 500 KB total. For web uploads (social media, websites), 200–400 KB is typical. For printing, use quality 85 or higher, or keep the original file. If you're not sure, start at quality 75 and look at the preview. If it looks good on your screen, it's probably fine.

Save a backup before you compress, because JPEG compression is permanent

Once you save a JPEG at a lower quality setting, you cannot get the lost detail back. If you compress a file to quality 70 and then later want to use it at quality 90, the result will still look like a quality-70 image — the detail is gone. Always keep a copy of the original file before you compress.

The easiest way is to create a folder called "Originals" and copy your uncompressed JPEGs there before you start. Then compress the copies in a separate folder. If you use cloud storage like Google Drive or OneDrive, you can keep the originals there and work with compressed versions on your computer.

If you're working with images you plan to edit (crop, adjust colors, resize), compress them last, after all editing is done. Each time you save a JPEG, you lose a little detail, so minimizing the number of times you save the same file keeps quality as high as possible.

Frequently Asked Questions

How much smaller will my JPEG be if I compress it?

It depends on the original quality and what quality you choose. Most JPEGs from phones or cameras are already compressed to quality 75–80. Compressing further to quality 70 might reduce file size by 20–30%. Reducing dimensions (width and height) usually shrinks file size more than adjusting quality alone — cutting width in half reduces file size to about one-quarter.

Will I see a difference between quality 75 and quality 85?

Probably not on a phone or computer screen. The difference becomes visible when you zoom in or print the image at large sizes. For web and email, quality 75 is usually fine. For anything you might print or edit later, use 85 or higher.

Can I compress a JPEG multiple times?

Yes, but each compression removes more detail. Compressing once to quality 70 looks acceptable. Compressing that same file again to quality 70 will look worse because you're compressing already-compressed data. Always compress once from the original if possible.

What's the difference between reducing dimensions and lowering quality?

Reducing dimensions removes pixels from the image, making it physically smaller. Lowering quality removes detail within the pixels that remain. For a photo you're sharing on social media, reducing dimensions is usually better because the image stays sharp. For a photo you might print, lowering quality is better because you keep the full resolution.

Is it safe to use online compression tools with personal photos?

Most online tools delete files from their servers after a few hours, but you're still uploading to someone else's computer. If the photo contains sensitive information or you're concerned about privacy, compress on your own device using Paint, Preview, or a downloaded tool instead.