How to reduce JPG file size

Start with the right quality range

JPEG quality is a number from 1 to 100, but it is not a percentage of the original. Each encoder maps the number to its own compression tables, so quality 80 in one app is not quality 80 in another.

For most photos, settings around 85 to 92 look identical to the original at normal viewing size, and 70 to 80 saves much more with little visible change. Below about 60, blocky squares and smearing around edges start to show, especially in skies, gradients and text.

Why the encoder matters

Compress JPG uses MozJPEG, an encoder tuned to make smaller files than the standard libjpeg at the same visual quality, often by 10 percent or more. It writes progressive JPEGs by default. A progressive JPEG appears as a rough full image that sharpens as it loads, instead of drawing from top to bottom, and for photos it is often slightly smaller too.

Check what you are starting with

If a JPEG was already saved at low quality, compressing it again mostly adds a second layer of artifacts. JPEG Quality estimates the setting a file was saved with by reading its quantization tables. Treat the number as an estimate: if it is already around 75 or lower, resizing or changing format will usually save more than lowering quality further.

Resize before you compress

Pixel count matters more than quality. Halving the width and height leaves a quarter of the pixels to store, which usually saves far more than any quality setting. A photo shown 1200 pixels wide on a web page needs about 1200 pixels, or up to about 2400 for sharp display on high-density screens. Resize Image uses Lanczos3 resampling by default for sharp downscaling.

When to leave JPG behind

If the image is going on a website you control, WebP at similar visual quality is typically 25 to 35 percent smaller, and every current browser displays it. Keep JPG for email, printing, upload forms and older software, where it is still the safest choice.

JPG cannot store transparency. If you need a transparent background, use PNG, WebP or AVIF instead.

Limitations

• Every lossy save discards a little more detail. Work from the original each time instead of compressing compressed copies.
• Removing EXIF data usually saves only a few kilobytes, sometimes tens of kilobytes when a camera embedded a large preview.
• Quality numbers are not comparable between apps, so judge by eye and by file size rather than by the number.