What "adjusting" a JPEG actually means

When you adjust a JPEG size, you are doing one of two things: making the image file smaller so it takes up less storage or bandwidth, or changing the dimensions (width and height in pixels) so it fits a specific space. These are not the same operation, and which one you need depends on what you are trying to do.

Shrinking the file size without changing dimensions is called compression. You are throwing away some of the color information the camera or editor captured, but the image still looks roughly the same at normal viewing distances. Changing the dimensions is called resizing. You are literally making the image smaller or larger in pixels, which changes how much space it takes up on screen or in print.

Most of the time, when someone says they need to "adjust" a JPEG, they mean compression — they want to email it, upload it to a website, or fit more photos on their phone without the image looking obviously worse. That is the focus here.

Key Takeaways

  • JPEG compression trades image quality for file size; you choose where that balance sits by adjusting the quality slider, usually from 1 to 100.
  • Most photos look fine at quality 75 to 85 when viewed on screen, and you can go lower (60 to 70) if the image is small or will be viewed from a distance.
  • Free tools like IrfanView (Windows), Preview (Mac), or online converters like TinyJPG let you compress without installing software.
  • Resizing (changing pixel dimensions) requires a different tool than compression, and you should resize before compressing to avoid doing the work twice.
  • Once you save a JPEG at low quality, you cannot get the lost detail back, so keep the original file and save the compressed version with a new name.

Compressing a JPEG on Windows

The simplest path on Windows is IrfanView, a free image viewer that handles compression without the learning curve of Photoshop. read it from irfanview.com, install it, then right-click any JPEG and choose "Open with IrfanView". Go to File > Save As, and a dialog will appear with a Quality slider. Drag it left to compress more (smaller file, lower quality) or right to keep more detail. Start at 80 and look at the preview; if it looks acceptable, save it with a new filename like "photo-compressed.jpg".

If you want to see the file size before you save, IrfanView shows it at the bottom of the Save dialog. A typical phone photo (3000 × 2000 pixels) at quality 80 usually compresses from 3 to 5 MB down to 500 KB to 1 MB. The exact number depends on how much detail is in the image — a photo of a blank wall compresses much more than one of a crowded street.

For bulk compression of many files at once, use IrfanView's Batch Conversion feature (File > Batch Conversion). Select all the JPEGs you want to compress, set the quality, and let it run through them. This saves time if you have dozens of photos to shrink.

Compressing a JPEG on Mac

Mac's built-in Preview app handles JPEG compression without installing anything. Open the image in Preview, go to File > Export, and a dialog appears. Change the Format dropdown to JPEG if it is not already there. Below that is a Quality slider; drag it left to compress more. The preview updates as you move it, so you can see the trade-off in real time. Save it with a new name.

If you prefer a visual comparison, Preview also lets you open two windows side by side — the original in one, the compressed version in the other — so you can judge whether the quality loss is acceptable before you commit. Just open the file twice and arrange the windows.

Using an online tool if you do not want to install anything

TinyJPG (tinyjpg.com) and Compressor.io (compressor.io) are free online tools that compress JPEGs in your browser. Drag a JPEG onto the page, and it compresses automatically. You can usually adjust the quality slider before downloading the result. These tools work on any device with a web browser, and your image is deleted from their servers after a few hours, though you should read their privacy policy if you are compressing sensitive photos.

The trade-off with online tools is that you are uploading your image to someone else's server. For most people this is fine — a vacation photo or a screenshot does not need to stay private. But if you are compressing medical records, financial documents, or anything you would not want stored on the internet, use a tool on your own computer instead.

Resizing (changing pixel dimensions) if you also need to make the image smaller on screen

If you need the image to be smaller in width and height — for example, to fit a specific space on a website or to make it print at a smaller size — you are resizing, not just compressing. IrfanView and Preview both do this, but the steps are different.

In IrfanView, go to Image > Resize/Resample. Enter new width and height values (the chain link icon keeps the proportions locked so you do not stretch the image). Then save as usual. In Preview, go to Tools > Adjust Size and enter the new dimensions. Resize before you compress, because compressing a smaller image is faster and you avoid processing the same pixels twice.

A common mistake is to resize a JPEG, save it, then resize it again later. Each time you save a JPEG, you lose some quality to compression. If you think you might need different sizes later, resize to the largest size you will ever need, compress once, and save that. Then resize down from the original if you need a smaller version.

Choosing a quality level that works for your use

The right quality setting depends on where the image will be seen and how large it will appear. A photo displayed at thumbnail size on a website can be quality 60 and still look fine; the same photo printed at 8 × 10 inches should be quality 85 or higher. Here are rough starting points:

  • Email or messaging (small on screen): Quality 70 to 75. File size matters more than detail because the image is small.
  • Website or social media (medium on screen): Quality 75 to 85. Most people view on phones or tablets, and compression artifacts become visible above that size.
  • Printing or large display: Quality 85 to 90. Compression becomes visible when the image is large, so keep more detail.
  • Archive (you might need it later): Quality 90 or higher, or keep the original uncompressed file. You cannot add detail back once it is gone.

The only way to know if a quality level works is to look at the result on the device or in the context where it will actually be used. A photo that looks fine on your phone might look blurry on a monitor. Always check before you delete the original.

Why you should keep the original file

JPEG compression is lossy, meaning it throws away information that cannot be recovered. Once you save a JPEG at quality 60, you cannot open it later and increase the quality to 85 — the detail is gone. For this reason, keep your original file (or a high-quality version at 90+) and save compressed versions with different names like "photo-web.jpg" or "photo-email.jpg".

If you shoot photos on a phone or camera, the original file is usually already a JPEG, and it is already compressed. You are not losing anything by compressing it further for email or web — the original is still on your device. But if you edit a photo in Photoshop or another editor, save the edited version as a TIFF or PNG (which do not compress) before you save a JPEG for sharing. That way you have the full-quality edited version if you need to make changes later.

Frequently Asked Questions

How much can I compress a JPEG before it looks bad?

It depends on the image and the viewing distance. A landscape photo with soft colors can drop to quality 70 and still look fine on screen. A photo with sharp text or fine details needs quality 80 or higher. The only reliable test is to compress it, look at it in the context where it will be used, and adjust if needed.

Can I make a JPEG smaller without losing quality?

No. JPEG compression always loses some information. If you need to shrink a file without any quality loss, use PNG or TIFF format instead — they compress without throwing away detail, but the files are usually larger. JPEG is a trade-off: smaller files in exchange for some visible quality loss.

What is the difference between quality 75 and quality 85?

Quality 85 keeps more color detail and is less likely to show visible compression artifacts (blocky areas or color banding). Quality 75 is noticeably smaller in file size. For most screen viewing, the difference is not obvious, but for printing or large displays, quality 85 is safer. Test both on your specific image to decide.

Do I need special software, or can I use what I already have?

If you are on Mac, Preview is built in and handles compression fine. On Windows, you likely have nothing built in, so IrfanView (free) is the easiest option. If you do not want to install anything, an online tool like TinyJPG works in any browser, though your image goes to their server temporarily.

What if I compress a JPEG and it looks worse than I expected?

Go back to your original file and try a higher quality setting. You cannot improve a file that is already compressed, so always start from the original. If you did not keep the original, you will have to re-shoot or re-edit the image.