Photo compression quality: what setting should you use?

When you compress a photo, the first question is usually what quality number to pick. For JPG and WebP, a good starting point is 75: check the result up close, and only go lower if you still need a smaller file. If you’d have to drop the quality a lot to hit your target, reduce the width and height in pixels first.

What the quality number actually means

Quality controls how strongly a lossy format such as JPG, WebP or AVIF is compressed. Most tools use a scale from 0 to 100. Lower numbers give smaller files and lower image quality. PNG is lossless, so it has no quality setting.

The number is not a percentage of the original quality. Google’s web.dev notes that not every tool interprets a value of “75” the same way, and that perceived quality always depends on what’s in the image. So don’t copy a number from another app and expect the same result. Look at what the tool you’re using actually produces.

That’s also why one tool may use different defaults for different formats. In ZEKILO Studio’s Compress Image, the default is 75 for JPG and WebP and 50 for AVIF. For reference, cwebp, the WebP encoder Google publishes, also defaults to a quality of 75.

Quality vs file size: measured results

Here’s the same test image (4000×3000 JPG, 4.0 MB) processed with different quality and size settings.

What we did	Result dimensions	File size
Compress Image, Quality 75 (default)	4000×3000	429 KB (−89%)
Compress Image, Quality 60	4000×3000	167 KB
Resize Image, width 1920px (JPG quality 90)	1920×1440	199 KB
Resize Image, long side 1080px (JPG quality 90)	1080×810	41 KB

Measured in desktop Chrome; results vary by device and browser. The test image is synthetic, so real photos may shrink by different amounts.

Dropping the quality from 75 to 60 took the file from 429 KB to 167 KB. But keeping the quality high at 90 and resizing to 1920px wide gave 199 KB. If you know how big the photo will be shown, resizing it to that size lets you cut the file size without lowering the quality much.

web.dev adds that when an image is displayed smaller than its actual size, it’s usually safe to compress a little more than you think would be noticeable. For photos you’ll print or view zoomed in, check the result at full size.

A simple way to choose

1. Start with the default. Compress at 75 for JPG and WebP, or 50 for AVIF. Zoom in and check whether text and lines look smudged, or whether smooth areas like sky look blotchy.
2. If you have a size limit, lower the quality step by step. If the file is still over the limit, lower it a little and check again. If blurring starts to show and the file is still too big, reduce the pixel dimensions instead. For forms and applications, see Resize photos for online applications.
3. For photos on a web page, you can also check with Lighthouse, Chrome’s page audit tool. Since Lighthouse 13, its “Improve image delivery” insight estimates how much each image could save by comparing its download size with an efficient bytes-to-pixel ratio for its format. Images with estimated savings under 4 KiB aren’t flagged.

Keep text, charts and logos as PNG

According to web.dev, JPEG encodes images in blocks of eight by eight pixels, so with too much compression the seams between the blocks can start to show. For screenshots, charts and logos, where text and lines need to stay crisp, keep the PNG and pick a PNG handling method instead.

Our test PNG (800×600 with a transparent background, 204 KB) became 32 KB (−84%) with Lossless optimization and 9 KB (−96%) with Reduce colors. Measured in desktop Chrome; results vary by device and browser. Reduce colors is lossy and cuts the image down to 256 colors or fewer, so colorful images like photos may show banding in smooth areas.

When lowering the quality doesn’t help

• Photos already saved at low quality may not get any smaller. If the result is the same size as the original or larger, Compress Image shows “This file is already optimized. We recommend keeping the original.” and makes [Download original] the main button.
• If the width and height are larger than you need, shrink them first with Resize Image.
• If the recipient supports it, you can also switch formats. See JPG vs PNG vs WebP for how the formats differ.

How to do it with ZEKILO Studio

1. Open Compress Image and drag and drop photos or pick them with [Choose files]. Compression starts right away with the defaults, and files never leave your device.
2. Move the [Quality] slider. The photos are compressed again automatically, and the file size and reduction update right away. For PNG, pick [Lossless optimization] or [Reduce colors] under [PNG handling].
3. Check the result and save it with [Download]. For several photos, use [Download all (ZIP)] to get them in one go.

To go smaller, reduce the pixel size with Resize Image. If you need a different format, use Image Converter. Compressed files don’t keep metadata such as GPS location, so keep the original if you need details like the date taken.

Summary

• Tools interpret quality numbers differently, so start with the default (75 for JPG and WebP, 50 for AVIF) and check the result with your own eyes.
• With our test image, quality 75 gave 429 KB and quality 60 gave 167 KB. Resizing to 1920px wide at quality 90 gave 199 KB.
• When you need a much smaller file, reduce the pixel size before you lower the quality, and keep text, charts and logos as PNG.