JPEG compression — Settings and quality

Worked example

JPEG compression has a single control, a Quality slider from 20 to 95 that starts at 78, so the job is choosing the number that fits the use.

As a starting map for photographs: 85 to 90 for a portfolio or hero image where detail sells the work, 75 to 80 for ordinary web pages and listings, 60 to 70 for email attachments and small thumbnails, and below 50 expect blocky areas on skin and skies. The slider tops out at 95 because pushing a JPEG close to its ceiling saves little while keeping most of the weight.

The steps are not even. Moving from 95 down to 85 often removes a large share of the bytes with hardly any visible change, while 60 to 40 trims much less but damages the image far more. That is why a step from 78 to 70 is usually a better experiment than from 40 to 30.

Remember what the slider does not touch. Pixel dimensions stay identical, so a 4032 × 3024 photo remains 4032 × 3024 and may still be too heavy for a small slot. If a 12-megapixel photo is going into a 1200 px wide column, resize first and then compress, which saves far more than quality alone.

The quality scale belongs to the browser encoder, so 78 here will not produce the same file as 78 in a desktop editor. Judge by the result, not the number. If the new JPEG is not smaller than your original, the tool keeps the original file rather than giving you a heavier copy.

JPEG photograph; original retained

JPEG export; compare bytes and edges

Because the slider starts at 78, test one step either side before accepting the first result.